• Preheat the oven to 350°F. Spray a 9x13 baking dish with baking spray, set aside.
• Get out and measure all of your ingredients.
  
• In a medium-sized bowl, add flour, baking powder, salt, and baking soda
  
• Stir until blended. Set aside.
  
• In the body of a stand mixer with the paddle attachment, cream the butter with the sugar for 3 minutes until light and fluffy.
  
• Scrape down the sides as needed.
  
• Add the egg whites into the mixer in three batches.
  
• Mixing fully before the next addition, scrape down the sides.
  
• Slowly stir in the milk and vanilla until smooth.
  
• Add half of the flour mixture.
  
• Mix in until combined.
  
• Mix in half of the sour cream.
  
• Repeat with the remaining flour and sour cream. Scrape down the sides and stir until blended.
  
• Add sprinkles.
  
• Stir until blended.
  
• Pour the batter into the baking dish and smooth out the top. Bake for 35-42 minutes until a toothpick inserted into the center comes out clean.
  
• Place on a wire rack to cool completely.
  

Frosting

• While the cake is cooling, make the frosting by placing the butter into a large bowl.
  
• Using an electric hand mixer and whip until smooth.
  
• Slowly add the powdered sugar 1 cup at a time.
  
• Until incorporated.
  
• Add the salt, milk, and vanilla, stir it in until combined then whip it on medium-high speed.
  
• Until light and fluffy for 3 minutes.
  
• Frost the cake using a butter knife or spatula.
  
• Add more sprinkles if desired.
  
• Slice and serve.
  
• Enjoy every bite.