Grease and flour (3) 8” round cake pans; set aside. Preheat oven to 325°F.

In a medium bowl, sift together the flour, baking powder and salt; set aside.

In a separate bowl, whisk together the milk, sour cream and vanilla extract; set aside.

Using a countertop mixer fitted with the paddle attachment, cream together the butter and sugar until light and fluffy (~3-4 minutes on medium-high speed).

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

Add the milk mixture to the bowl. Mix on low until well combined.

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

In a separate bowl, beat egg whites on medium speed until stiff peaks form. Carefully fold the egg whites into the cake batter until fully mixed.

Divide the batter evenly between the 3 cake pans. Bake at 325°F for 30-32 minutes, or until a toothpick inserted into the center of the cake comes out clean.

Using a medium saucepan, melt butter completely over medium heat. Add brown sugar and heavy cream; continue cooking over medium heat, stirring occasionally, until well combined and sugar has completely dissolved.

Increase heat and bring to a boil; Boil for 1 minute, stirring constantly.

Remove from heat and let cool to room temperature. Transfer mixture into bowl of a countertop mixer. Add powdered sugar, one cup at a time, mixing completely after each addition. (Note: If frosting is too loose, add a couple more tbsps of powdered sugar. If frosting is too thick, add a tbsp of milk.)

Place one layer of cake on large platter. Spread ~1 cup of frosting on top. Repeat with 2nd and 3rd layers of cake. Use remaining frosting on top and sides of cake. Decorate as desired.