5-Ingredient Microwave Rhubarb Crisp in a Mug

If you ask me, dessert shouldn’t require turning on the oven.

This single-serving rhubarb crisp comes together in minutes using just your microwave and a mug. Tart rhubarb gets sweetened with a hint of orange zest and warm spices, then topped with a buttery oat crumble.

The filling bubbles up perfectly in the microwave while the topping gets just crispy enough to satisfy. A dollop of whipped cream and a sprinkle of cinnamon finish it off.

It’s an easy weeknight treat that feels special without any fuss, perfect for when you need something sweet right now.

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What Kind of Rhubarb Should I Use?

Fresh rhubarb is always your best bet for this recipe, and you’ll find it at most grocery stores during spring and early summer. The color of the stalks doesn’t really matter – both red and green rhubarb will taste great, though the red variety does make for a prettier presentation. If fresh rhubarb isn’t available, frozen rhubarb works just fine too. Just make sure to thaw it first and drain off any excess liquid so your mug crisp doesn’t end up too watery.

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Options for Substitutions

This quick mug dessert is easy to customize based on what you have in your kitchen:

• Rhubarb: Fresh rhubarb works best, but frozen rhubarb is totally fine – just thaw it first and drain any excess liquid. You can also mix in some diced strawberries or apples for a different flavor combo.
• Orange zest: Don’t have an orange? Lemon zest works just as well, or you can skip the citrus altogether and add a pinch of nutmeg instead.
• Oats: Old-fashioned rolled oats are ideal here, but quick oats will work in a pinch. Just avoid instant oatmeal packets as they’re too processed for a good crisp topping.
• Butter: You can swap the butter with coconut oil for a dairy-free version. Just make sure it’s solid, not melted, when you mix it into the topping.
• Brown sugar: If you’re out of brown sugar, use all granulated sugar and add a tiny splash of molasses, or just use granulated sugar on its own – it’ll still taste great.
• Whipped cream: Regular whipped cream, vanilla ice cream, or even Greek yogurt make excellent toppings instead of light whipped cream.

Watch Out for These Mistakes While Cooking

The biggest mistake when making mug desserts is overcooking them in the microwave, which can turn your rhubarb rubbery and the topping hard as a rock – start with 2 minutes and add 30-second intervals if needed, since every microwave has different power levels.

Another common error is skipping the cooling time, but waiting at least 5 minutes before digging in allows the filling to thicken up properly and prevents you from burning your mouth on molten-hot fruit.

To get a crispier topping instead of a soggy one, make sure your butter is cold when you mix it into the oat mixture, and use your fingers to create pea-sized crumbles rather than stirring it into a paste.

Finally, don’t pack your rhubarb too tightly into the mug – leave a little room at the top for the filling to bubble up during cooking, or you’ll end up with a mess in your microwave.

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What to Serve With Rhubarb Crisp in a Mug?

This mug crisp is already pretty complete on its own, but a scoop of vanilla ice cream on top takes it to the next level – the cold ice cream melting into the warm crisp is absolutely delicious. If you’re not in the mood for ice cream, a dollop of whipped cream or even some Greek yogurt adds a nice creamy contrast to the tart rhubarb. For a cozy afternoon treat, pair your mug crisp with a hot cup of coffee or tea, which complements the warm cinnamon flavors perfectly. You could also drizzle a bit of caramel sauce over the top if you’re feeling fancy and want some extra sweetness.

Storage Instructions

Best Fresh: This microwave rhubarb crisp is really meant to be enjoyed right away while it’s still warm and the topping is nice and crispy. The texture changes quite a bit once it sits, so I’d recommend making it fresh whenever you get a craving.

Short-Term Storage: If you do have leftovers, you can cover the mug with plastic wrap and keep it in the fridge for a day or two. Just know that the oat topping will get soft and lose its crunch, but the flavors will still be good.

Warm It Up: Pop your leftover crisp back in the microwave for about 30 seconds to warm it through. It won’t be quite as crispy as when it was fresh, but it’ll still taste great with a dollop of whipped cream on top.

Estimated Nutrition

Estimated nutrition for the whole recipe (without optional ingredients):

• Calories: 220-270
• Protein: 2-3 g
• Fat: 6-9 g
• Carbohydrates: 43-50 g

Ingredients

For the rhubarb filling:

• 1 cup rhubarb (cut into 1/2-inch pieces for even cooking)
• 3/4 tsp vanilla (I always use Nielsen-Massey for the best aroma)
• 1 1/2 tbsp sugar
• 1 1/2 tbsp brown sugar
• 1/4 tsp orange zest
• 1/2 tsp cinnamon
• 1 tbsp flour
• 1 pinch ground nutmeg

For the crisp topping:

• 3 tbsp oats (I prefer Quaker Old Fashioned oats for a better chew)
• 1 tbsp flour
• 1 1/2 tbsp brown sugar
• 1/2 tbsp sugar
• 3/4 tsp cinnamon
• 1 1/2 tbsp butter (melted and cooled to room temperature)

For the garnish (optional):

• 2 tbsp whipped cream (optional but recommended for extra richness)
• 1 dash cinnamon

Step 1: Prepare the Rhubarb Filling

• 1 cup rhubarb
• 1 1/2 tbsp sugar
• 1 1/2 tbsp brown sugar
• 3/4 tsp vanilla
• 1/4 tsp orange zest
• 1/2 tsp cinnamon
• 1 tbsp flour
• 1 pinch ground nutmeg

In a small bowl, combine the cut rhubarb pieces with both sugars, vanilla extract, orange zest, cinnamon, flour, and nutmeg.

Stir until the rhubarb is evenly coated with the sugar mixture and the flour is fully incorporated.

This coating helps the rhubarb release its juices and thicken the filling as it cooks.

Transfer the mixture directly into a microwave-safe mug, pressing it down gently to create an even layer.

Step 2: Make the Crispy Topping

• 3 tbsp oats
• 1 tbsp flour
• 1 1/2 tbsp brown sugar
• 1/2 tbsp sugar
• 3/4 tsp cinnamon
• 1 1/2 tbsp butter

In a separate small bowl, combine the oats, flour, brown sugar, sugar, and cinnamon.

Pour the melted and cooled butter over the dry ingredients and stir until the mixture is crumbly and evenly moistened.

I prefer using old-fashioned oats here because they stay chewy and substantial rather than turning into paste during the short microwave time.

The butter should coat all the ingredients without making it wet or clumpy.

Step 3: Assemble and Microwave

• rhubarb filling from Step 1
• crispy topping from Step 2

Spread the crispy topping mixture evenly over the rhubarb filling in the mug, using the back of a spoon to distribute it in an even layer.

Microwave on high for 2 to 3 minutes—start checking at 2 minutes to see if the butter has melted and the filling is bubbling around the edges.

The mug will be very hot when it comes out, so use caution when removing it from the microwave.

Step 4: Cool and Serve

• 2 tbsp whipped cream
• 1 dash cinnamon

Let the crisp cool for a few minutes before eating—this allows the filling to set slightly and makes it easier to enjoy without burning your mouth.

For extra richness and to balance the tartness of the rhubarb, top with a dollop of whipped cream and a light dusting of cinnamon.

I find the cream really transforms this into something special and worth the extra step.

5-Ingredient Microwave Rhubarb Crisp in a Mug

Delicious 5-Ingredient Microwave Rhubarb Crisp in a Mug recipe with step-by-step instructions.

Print Recipe Pin Recipe

Prep Time 5 minutes mins

Cook Time 10 minutes mins

Total Time 17 minutes mins

Servings 1 serving

Calories 245 kcal

Ingredients

  

For the rhubarb filling::

• 1 cup rhubarb (cut into 1/2-inch pieces for even cooking)
• 3/4 tsp vanilla (I always use Nielsen-Massey for the best aroma)
• 1 1/2 tbsp sugar
• 1 1/2 tbsp brown sugar
• 1/4 tsp orange zest
• 1/2 tsp cinnamon
• 1 tbsp flour
• 1 pinch ground nutmeg

For the crisp topping::

• 3 tbsp oats (I prefer Quaker Old Fashioned oats for a better chew)
• 1 tbsp flour
• 1 1/2 tbsp brown sugar
• 1/2 tbsp sugar
• 3/4 tsp cinnamon
• 1 1/2 tbsp butter (melted and cooled to room temperature)

For the garnish (optional)::

• 2 tbsp whipped cream (optional but recommended for extra richness)
• 1 dash cinnamon

Instructions

 

• In a small bowl, combine the cut rhubarb pieces with both sugars, vanilla extract, orange zest, cinnamon, flour, and nutmeg. Stir until the rhubarb is evenly coated with the sugar mixture and the flour is fully incorporated. This coating helps the rhubarb release its juices and thicken the filling as it cooks. Transfer the mixture directly into a microwave-safe mug, pressing it down gently to create an even layer.
• In a separate small bowl, combine the oats, flour, brown sugar, sugar, and cinnamon. Pour the melted and cooled butter over the dry ingredients and stir until the mixture is crumbly and evenly moistened. I prefer using old-fashioned oats here because they stay chewy and substantial rather than turning into paste during the short microwave time. The butter should coat all the ingredients without making it wet or clumpy.
• Spread the crispy topping mixture evenly over the rhubarb filling in the mug, using the back of a spoon to distribute it in an even layer. Microwave on high for 2 to 3 minutes—start checking at 2 minutes to see if the butter has melted and the filling is bubbling around the edges. The mug will be very hot when it comes out, so use caution when removing it from the microwave.
• Let the crisp cool for a few minutes before eating—this allows the filling to set slightly and makes it easier to enjoy without burning your mouth. For extra richness and to balance the tartness of the rhubarb, top with a dollop of whipped cream and a light dusting of cinnamon. I find the cream really transforms this into something special and worth the extra step.