Crumb Topped Banana Muffins

INGREDIENTS

• 1 1/2 cups flour
• 1 teaspoon baking soda
• 1 teaspoon baking powder
• 1/2 teaspoon salt
• 3 large ripe bananas, mashed
• 3/4 cup sugar
• 1 egg, lightly beaten
• 1/3 cup butter, melted
• 1/3 cup packed brown sugar
• 1 tablespoon flour
• 1/8 teaspoon cinnamon, to taste
• 1 tablespoon cold butter
• 1/4 cup nuts, chopped (optional)