My Grandmother's Heavenly Banana Muffins

Ingredients

• 3 medium ripe bananas (approximately 1 ½ cups mashed, 450g)
• ⅓ cup unsalted butter, melted (75g)
• ½ cup granulated sugar (100g)
• 1 large egg, beaten
• 1 teaspoon vanilla extract
• 1 teaspoon baking soda
• Pinch of salt
• 1 teaspoon ground cinnamon (optional)
• 1 ½ cups all-purpose flour (190g)
• ½ cup chopped walnuts or pecans (optional, 70g)
• ½ cup chocolate chips (optional, 90g)