White Chocolate Christmas Tree Cupcakes

Ingredients

• 2 1/2 cups all-purpose flour
• 2 tablespoons cornstarch
• 1 teaspoon baking powder
• 1/2 teaspoon baking soda
• 1 teaspoon salt
• 6 ounces white chocolate, finely chopped
• 1/2 cup hot water
• 1 cup (2 sticks) butter, softened
• 1 3/4 cups granulated sugar
• 4 eggs, separated
• 1 teaspoon vanilla extract or vanilla bean paste
• 1 cup milk + 2 teaspoons lemon juice, prepared ahead
• 1 cup (2 sticks) unsalted butter, room temperature
• 3-4 cups powdered sugar, sifted
• 1 1/2 teaspoons vanilla extract
• 2-3 tablespoons milk
• green royal icing
• sugar ice cream cones