Preheat your oven to 350°F and grease a 9-inch springform pan or similar 9x13 inch baking dish with butter or cooking spray. Bring your cream cheese (all 21 oz total), eggs, and sour cream to room temperature—this ensures a smooth, lump-free cheesecake layer and carrot cake that rises evenly. Finely shred your carrots and set aside. Sift your powdered sugar to remove any lumps, which will give you a silky frosting.

In a bowl, combine 18 oz room-temperature cream cheese with 3/4 cup sugar and 2 tsp flour, beating until completely smooth and creamy—this prevents lumps in your cheesecake. Add 2 room-temperature eggs one at a time, then 1 1/4 tsp vanilla essence and 1/2 cup sour cream, mixing until just combined. Tap the bowl firmly on the counter several times to release any air bubbles, which would create tunnels in the finished cake.

In one bowl, whisk together 1 1/2 cups flour, 1/2 tsp baking soda, 1/2 tsp baking powder, 1/4 tsp salt, 1 1/4 tsp cinnamon, 1/4 tsp nutmeg, and 1/4 tsp ground ginger—set this dry mixture aside. In another bowl, combine 1/2 cup canola oil, 1/4 cup applesauce, 2/3 cup sugar, 1/3 cup brown sugar, 2 room-temperature eggs, and 1 tsp vanilla essence, beating for about 1 minute until well emulsified. I like to use applesauce here instead of extra oil because it keeps the cake moist without making it greasy.

Fold the dry ingredient mixture from Step 3 into the wet oil mixture, stirring until just combined, then fold in the 1 1/3 cups shredded carrots until evenly distributed. Tap the bowl on the counter to remove air bubbles. Pour 1 1/2 cups of the carrot batter into your prepared pan and spread evenly. Pour about 1/3 of the cheesecake mixture from Step 2 over the carrot layer, then add the remaining carrot batter, and finish with the remaining cheesecake mixture on top, allowing layers to settle naturally.

Bake for 40 minutes uncovered, then tent the top loosely with foil to prevent over-browning, and continue baking for another 20-25 minutes until the cheesecake is set but still has a slight jiggle in the center when you gently shake the pan—this residual heat will continue cooking it as it cools. The cake should reach about 160-165°F in the center when tested with a thermometer. Remove from oven and let cool to room temperature (about 1 hour), then refrigerate for at least 6 hours or overnight before frosting.

In a bowl, beat 3 oz room-temperature cream cheese with 1 1/2 tbsp butter (I prefer Kerrygold for its rich flavor) until creamy. Gradually add the sifted powdered sugar from Step 1, 6 tbsp sour cream, and 1/2 tsp vanilla essence, beating for 4-5 minutes until light, fluffy, and spreadable. The longer mixing time incorporates air, giving you a silky frosting that's easier to spread evenly.

Remove the chilled cake from the refrigerator and spread the frosting from Step 6 evenly over the top using an offset spatula or knife. Freeze for 20-30 minutes to let the frosting set slightly, then toast or roughly chop the 1/2 cup pecans and press them gently into the frosting around the edges or scatter them across the top for texture and flavor. Slice with a sharp, warm knife (wiped between cuts) and serve chilled.