Best Banana Muffins with Streusel Topping

Ingredients

• 1 1/2 cups all-purpose flour
• 1 teaspoon baking powder
• 1 teaspoon baking soda
• 1 teaspoon ground cinnamon
• 1/2 teaspoon salt
• 1/4 teaspoon ground nutmeg
• 1 1/2 cups mashed ripe bananas (about 3 large ripe bananas)
• 1 large egg
• 2/3 cups packed brown sugar
• 3 tablespoons unsalted butter, melted
• 3 tablespoons vegetable oil
• 2 tablespoons buttermilk
• 1/2 teaspoon vanilla extract
• 1/2 cup all-purpose flour
• 1/2 cup packed brown sugar
• 1/4 cup unsalted butter, cold
• 1/2 teaspoon ground cinnamon
• 1/4 teaspoon salt