Ingreadient

• 1 1/2 cups all-purpose flour
• 3 tablespoons confectioners' sugar
• 2 teaspoons baking powder
• 1/2 teaspoon kosher salt
• 1 1/4 cups milk
• 1 large egg yolk, plus 3 egg whites
• 4 tablespoons unsalted butter, melted and cooled, plus more for brushing
• 1/2 teaspoon pure vanilla extract
• butter and maple syrup, for serving