Preheat the oven to 350 degrees. In a stand mixer or large bowl, combine the cake mix, pudding mix, sour cream, oil, applesauce, beaten eggs, and water.
Line 18 muffin tins with cupcake liners. Pour about 1/4 cup batter into each tin, filling about 3/4 of the way.
Bake for 25 minutes or until top is springy with touch and a toothpick comes out clean. Let cool in the muffin tin for an hour before removing.
Puree the strawberries until smooth. Add to a small saucepan over medium heat. Cook the strawberry puree, whisking often, until the mixture reduces by half. Let come to room temperature.
In a stand mixer with the paddle attachment, add the butter and whip until soft and fluffy. Mix in 1 cup of powdered sugar, then add the strawberry puree and vanilla. Add the remaining 1 1/2 cups powdered sugar and mix until fluffy.
Frost the cupcakes once cool and serve!
Frosting inspiration from Cooking Classy.