Preheat the oven to 350°F (177°C). Line a 12-cup muffin pan with cupcake liners. Line a second pan with 2 liners—this recipe makes about 14 cupcakes. Set aside.

Whisk the cake flour, baking powder, baking soda, and salt together. Set aside.

Using a handheld or stand mixer fitted with a paddle attachment, beat the butter and sugar together on high speed until smooth and creamy, about 2 minutes. Scrape down the sides and up the bottom of the bowl with a rubber spatula as needed. Add the egg whites and vanilla extract. Beat on medium-high speed until combined, then beat in the sour cream. Scrape down the sides and up the bottom of the bowl as needed. With the mixer on low speed, add the dry ingredients until just incorporated. With the mixer still running on low, slowly pour in the milk until combined. Do not over-mix. Gently and slowly whisk in the sprinkles. The batter will be slightly thick.

Pour/spoon the batter into the liners. Fill only 2/3 full to avoid spilling over the sides. Bake for 19-22 minutes, or until a toothpick inserted in the center comes out clean. For around 30 mini cupcakes, bake for about 11-13 minutes, same oven temperature. Allow the cupcakes to cool completely before frosting.

Frost cooled cupcakes with vanilla buttercream. I tinted it with 1 drop Dusty Rose Gel Food Coloring and used Ateco 849 piping tip. You can watch me decorate the cupcakes in the video above.

Leftover cupcakes keep well covered tightly in the refrigerator for 3 days.