For the cake

1. Preheat oven to 350°F/177°C. Butter and flour a 8-inch square cake pan.  Line with parchment paper and set aside.
2. In a medium bowl, sift together flour, baking powder, baking soda and salt.  Set aside.
3. In a large bowl using a hand-held mixer or stand mixer fitted with the paddle attachment, beat together softened butter and sugar on medium-high speed until smooth and creamy, about 4-5 minutes.  Scrape down the sides of the bowl as needed.  Beat in egg whites, one at a time, until combined.  Scrape down the sides of the bowl and beat in vanilla and almond extracts until mixed well.  Add the sour cream and beat until combined.  With the mixer on low speed and in three parts, alternately add the dry ingredients and the milk to the batter, beginning and ending with the dry ingredients.  Beat until just combined.  Fold in sprinkles.
4. Fill prepared cake pan with batter and bake for 30-35 minutes, or until a toothpick inserted in the center comes out clean.
5. Allow cake to cool completely in the pan set on a wire rack before frosting.

For the frosting

1. In a large bowl using a hand-held mixer or stand mixer fitted with the paddle attachment, beat the butter on medium-high speed for 5 minutes.  With the mixer on low speed, slowly add in the powdered sugar and salt, beating until the sugar is completely incorporated.  Add the vanilla and almond extracts and beat until incorporated.  Add, one tablespoon at a time, the heavy cream until desired consistency is achieved.  Beat the buttercream on medium-high for an additional 5 minutes.