In a large mixing bowl, beat butter with sugar until creamy. Add egg and vanilla. Add mashed banana.
Add flour, baking powder, baking soda, and salt. Divide batter in half.
To one half of the batter, mix in the baking cocoa.
Prepare muffin tin by greasing. Drop 2 tablespoons of plain batter into each muffin cup. Then add 2 tablespoons of chocolate batter into each muffin cup. Bake at 350°F for 16-18 minutes.
Notes
Enjoy these moist and flavorful muffins as a quick breakfast or snack.