Birthday Cake: Bakery-Quality Crumb in 80 - My Recipe Critic

Ingredients

• 420g cake flour
• 400g granulated sugar
• 1.5 tbsp baking powder
• 1 tsp fine sea salt
• 225g unsalted butter, softened
• 6 large egg whites, room temperature
• 180ml whole milk
• 120g full fat sour cream
• 2 tsp vanilla bean paste
• 5 large egg whites (for buttercream)
• 300g granulated sugar (for buttercream)
• 450g unsalted butter, cubed and cool
• 1 tbsp vanilla extract
• 1 pinch salt