Preheat oven to 350°F. Prepare a muffin pan with liners.
Cream butter and sugar together. Mix in egg and vanilla until just combined. Add dry ingredients, followed by sour cream and banana. Mix until smooth. Remove 1/2C banana batter, mixing with 3oz melted chocolate.
To each muffin liner, add 1 medium scoop of banana batter, 1/2 small scoop chocolate batter, 1/2 scoop medium banana batter and finally 1/2 small scoop chocolate batter. Swirl gently with a toothpick. Bake for 20-25 minutes or until a toothpick inserted comes out clean. Cool in pan for 5 minutes, transfer to a wire rack to cool completely. Store in an airtight container.
Nutritional information is provided as a courtesy and is an estimate only. Nutrition information can vary for a variety of reasons. For the most accurate data, use your preferred nutrition calculator with the actual ingredients you used to make this recipe.
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