Preheat oven to 350°F.

Using a medium bowl, sift together the flour, baking powder and salt. Stir until well combined; set aside.

Using a countertop mixer fitted with the paddle attachment, cream together the butter and sugar until light and fluffy (~2-3 minutes on medium speed).

Add the egg and egg whites; mix on low speed until well combined.

Add half of the flour mixture to the bowl; mix on low speed until well combined.

Add the milk, sour cream and vanilla extract; mix on low speed until well combined. Add the remaining flour mixture; mix on low speed until well combined. (Tip: Don’t forget to scrape down the sides of the bowl to ensure all ingredients are fully mixed.)

Add rainbow sprinkles; mix until well combined.

Divide batter evenly into the two prepared cake pans.

Bake at 350°F for 24-28 minutes, or until a toothpick inserted into the center of the cake comes out clean.

Let cakes cool in pan for 10 minutes before turning out onto a cooling rack until completely cool.

Let the ice cream soften at room temperature for ~20 minutes, or until soft enough to spread easily.

Fold the sprinkles into the softened ice cream.

Wrap the entire cake (including pan) with plastic wrap and freeze for 3 hours or overnight.

Using a medium mixing bowl, add the whipping cream, powdered sugar and vanilla extract.

Use a hand mixer fitted with the whisk attachment to whip until stiff peaks form (~3-4 minutes).

Remove the cake from the pan and use an offset spatula to spread whipped cream around edges and on top of the cake.

Garnish top of cake with additional rainbow sprinkles.

Place cake back in freezer for ~3-4 more hours (preferably overnight) before slicing and serving.