Step 1: Brown the Butter - Melt 2 cups of unsalted butter in a light-colored saucepan over medium heat until golden brown and nutty, about 5-7 minutes. Refrigerate until solid.

Step 2: Prepare Cake Pans - Preheat oven to 350°F (175°C) and line three 8-inch or four 7-inch cake pans with parchment paper, making sure to grease them well.

Step 3: Mix Dry Ingredients - Sift together 2 ½ cups of all-purpose flour, 1 ½ cups of granulated sugar, 2 ½ teaspoons of baking powder, and ½ teaspoon of fine salt in a large mixing bowl.

Step 4: Blend Ingredients - Gradually add browned butter to dry mixture. Incorporate 4 egg whites, 1 cup sour cream, ½ cup vegetable oil, and 2 teaspoons vanilla extract, mixing until smooth.

Step 5: Bake - Divide batter among prepared pans and bake for 33-35 minutes, rotating halfway through. Cakes should be lightly golden and toothpick should come out clean.

Step 6: Cool Layers - Allow cakes to cool in pans for 10 minutes before transferring to a wire rack to cool completely.

Step 7: Make Frosting - Beat together 1 cup cooled browned butter and 8 oz cream cheese. Gradually mix in 4 cups powdered sugar, 1 teaspoon vanilla extract, a pinch of salt, and ¼ cup heavy cream.

Step 8: Assemble Cake - Place one cooled layer on a cake stand, spread frosting between layers, and cover the entire cake with the remaining frosting.