9-Inch Bottom Tier

• 3 and 2/3 cups (433g) cake flour (spoon & leveled)
• 1 teaspoon salt
• 1 teaspoon baking powder
• 3/4 teaspoon baking soda
• 1 and 1/2 cups (3 sticks; 345g) unsalted butter, softened to room temperature
• 2 cups (400g) granulated sugar
• 3 large eggs + 2 additional egg whites, at room temperature
• 1 Tablespoon pure vanilla extract (yes, Tbsp!)
• 3/4 cup (180g) full-fat sour cream, at room temperature
• 3/4 cup (180ml) whole milk, at room temperature

6-Inch Top Tier

• 1 and 3/4 cups (207g) cake flour (spoon & leveled)
• 1/4 teaspoon salt
• 3/4 teaspoon baking powder
• 1/4 teaspoon baking soda
• 1/2 cup (1 stick; 115g) unsalted butter, softened to room temperature
• 1 cup (200g) granulated sugar
• 1 large egg + 1 additional egg white, at room temperature
• 2 teaspoons pure vanilla extract
• 1/2 cup (120g) full-fat sour cream, at room temperature
• 1/2 cup (120ml) whole milk, at room temperature

Frosting for 9 inch cake & piping

• 2 cups (4 sticks; 460g) unsalted butter, softened to room temperature
• 8 cups (960g) confectioners’ sugar
• 6 Tablespoons (90ml) whole milk or heavy cream
• 1 and 1/2 teaspoons pure vanilla extract
• 1/8 teaspoon salt

Frosting for 6 inch cake

• 1 cup (2 sticks; 230g) unsalted butter, softened to room temperature
• 4 – 5 cups (480-600g) confectioners’ sugar
• 1/4 cup (60ml) heavy cream or whole milk
• 1 teaspoon pure vanilla extract
• salt, to taste