Fluffy Japanese Pancakes

Name: Fluffy Japanese Pancakes
Cook time: 40 min
Total time: 40 min
Cuisine: Asian, Japanese
Ingredients: 1 1/2 cups all-purpose flour (see Cook's Note); 3 tablespoons confectioners' sugar; 2 teaspoons baking powder; 1/2 teaspoon kosher salt; 1 1/4 cups milk; 4 tablespoons unsalted butter, melted and cooled, plus more for serving; 1/2 teaspoon pure vanilla extract; 1 large egg yolk plus 3 large egg whites; 1/4 teaspoon cream of tartar; Nonstick cooking spray; Maple syrup, for serving