Grandma's Fluffy Donuts with Cinnamon Sugar

Ingredients

• 1 1/2 cups all-purpose flour
• 1/2 cup granulated sugar
• 2 teaspoons baking powder
• 1/2 teaspoon baking soda
• 1/2 teaspoon salt
• 1 teaspoon ground cinnamon
• 1/2 teaspoon nutmeg (optional)
• 1/2 cup unsalted butter, melted
• 1 large egg
• 1/2 cup milk
• 1 teaspoon vanilla extract
• 1/4 cup granulated sugar
• 1 tablespoon ground cinnamon
• 1/4 cup unsalted butter, melted (for brushing)