White Mountain Layer Cake with Marshmallow Buttercream | Saveur

Ingredients

• 1 packet (2 1/4 tsp. | 1/4 oz.) unflavored gelatin powder
• ¹⁄₄ cup (2 oz.) cool tap water to bloom the gelatin
• 1 tbsp. vanilla extract and/or 1 vanilla bean
• ³⁄₄ cup (6 oz.) water for the sugar syrup
• ³⁄₄ cup plus 2 Tbsp. (10 oz.) light corn syrup
• 2 cups (14 1/2 oz.) sugar
• ¹⁄₂ tsp. Diamond Crystal kosher salt (half as much if iodized)
• 5 sticks (20 oz.) unsalted butter, soft but cool–about 65°F
• 4 cups (16 oz.) bleached cake flour such as Swans Down
• 2 sticks (8 oz.) unsalted butter, pliable but cool—about 65°F
• ²⁄₃ cup (4 oz.) virgin coconut oil, solid but cream–about 70°F
• 2 ¹⁄₄ cups (16 oz.) sugar
• 2 ¹⁄₂ tsp. baking powder
• 1 tsp. baking soda
• ³⁄₄ tsp. Diamond Crystal kosher salt (half as much if iodized)
• 1 cup (8 1/2 oz.) egg whites (from 8 large eggs), brought to about 70°F
• 2 tbsp. (1 oz.) vanilla extract
• 1 tsp. almond extract
• 2 cups (16 oz.) cultured low-fat buttermilk, brought to about 70°F