Prepare the Cake:

1. Preheat Oven and Prepare Pans:
   • Preheat your oven to 350°F (175°C). Grease and flour three 9-inch round cake pans, or line them with parchment paper.
2. Mix Dry Ingredients:
   • In a medium bowl, whisk together flour, baking powder, baking soda, and salt. Set aside.
3. Cream Butter and Sugar:
   • In a large bowl, beat softened butter until smooth. Gradually add granulated sugar and beat until light and fluffy.
4. Add Eggs and Vanilla:
   • Add eggs one at a time, beating well after each addition. Mix in vanilla extract.
5. Combine Wet and Dry Ingredients:
   • Add the flour mixture in three additions, alternating with buttermilk, beginning and ending with the flour mixture. Mix until just combined.
6. Fold in Egg Whites and Sprinkles:
   • Whisk egg whites until fluffy and holding soft peaks. Gently fold into the batter. Stir in sprinkles.
7. Bake the Cakes:
   • Divide the batter among the prepared pans. Bake for 25 to 30 minutes, or until a toothpick inserted in the center comes out clean.
8. Cool the Cakes:
   • Allow cakes to cool in pans for 10 minutes, then transfer to a wire rack to cool completely.

Prepare the Frosting:

1. Beat Butter:
   • Beat softened butter until smooth and creamy.
2. Add Sugar and Cream:
   • Gradually add confectioners’ sugar, heavy cream, vanilla extract, and salt. Beat until smooth and fluffy.

Assemble the Cake:

1. Frost the Cake:
   • Frost the cooled cakes as desired. Spread frosting between each layer, then cover the sides and top.
2. Decorate:
   • Garnish with additional sprinkles if desired.