Preheat your oven to 375°F and grease a standard 12-cup muffin tin. While the oven heats, prepare the crumble topping by combining the melted and cooled butter, brown sugar, sugar, cinnamon, nutmeg, and flour in a small bowl. Mix with a fork until the mixture becomes crumbly and resembles coarse breadcrumbs—this takes just a minute or two. Set the crumble aside so it's ready to top the muffins once they're filled.

In a large mixing bowl, beat the butter and sugar together for about 1 minute until the mixture is light and creamy. This process incorporates air into the batter, which helps the muffins rise evenly and develop a tender crumb.

Add the room-temperature eggs and vanilla to the butter mixture and beat until fully combined and smooth. Room-temperature eggs blend more easily and create a better emulsion, resulting in a more tender muffin.

In a separate bowl, whisk together the flour, baking powder, and salt. Add half of the dry mixture to the butter mixture from Step 3 and stir until just combined. Pour in the milk and stir gently, then add the remaining dry mixture and fold until no flour streaks remain. I like to use a gentle hand here—overmixing develops gluten and creates tough, dense muffins instead of tender ones.

Gently fold the finely chopped strawberries into the batter from Step 4 until evenly distributed—be careful not to crush the berries or overmix. Divide the batter evenly among the greased muffin cups, filling each about three-quarters full. Leave some room at the top for the crumble topping and for the muffins to rise.

Sprinkle a generous portion of the crumble topping from Step 1 onto each muffin, pressing it gently so it adheres to the batter. Bake in the preheated 375°F oven for 16 to 18 minutes, until a toothpick inserted into the center of a muffin (avoiding the strawberry pieces) comes out clean or with just a few moist crumbs. The tops should be golden brown and the crumble topping lightly crisped.

Let the muffins cool in the pan for about 5 minutes, then turn them out onto a wire rack. They're best enjoyed slightly warm or at room temperature. The crumble topping will continue to crisp up as they cool.