Banana Marble Cake

3 cups all purpose flour
1 tsp baking powder
1 tsp baking soda
1/2 tsp salt

1 1/2 cup sugar
1/2 cup vegetable oil or butter
3 eggs

1/4 cup milk
2 tbsp rice vinegar or lemon juice

3 ripe bananas or 1 1/2 cup
1 tbsp vanilla
4 tbsp cocoa powder

1. sift together the flour, baking powder, baking soda and salt.
2. combine the milk and vinegar then set aside
3. beat the sugar and butter or oil , add egg one at a time, beating until smooth, then add the mashed banana continue beating, add half of the dry ingredients let it mix, then pour the sour milk, then the remaining half of the dry ingredients, finally add the vanilla
4. place 1/3 of the batter in a separate bowl mix it with the cocoa powder.
5. scoop 2 teaspoon of batter into the lined muffin pan, then scoop a tablespoon of  cocoa batter then top again with some white batter again, use a toothpick or tip of the knife to make a swirl on top. (the batter should be 2/3 full )
6. bake at 350F oven for 20-25 mins , makes 16-18 cupcakes