Nutella-Stuffed Mini Pancakes

• 1 cup all-purpose flour

• 1 1/2 teaspoons sugar

• 1/2 teaspoon baking powder

• 1/4 teaspoon salt

• 2 eggs, yolks and whites separated

• 1 cup milk

• 2 tablespoons unsalted butter, melted and room temperature

• Cooking spray

• Nutella