Preheat the oven to 350°F. Line a muffin pan with baking cups or grease the muffin pan with cooking spray.
In a large bowl, whisk together the flour, sugar, brown sugar, baking powder, baking soda and salt.
In a separate medium bowl, whisk together the mashed bananas, vanilla extract, egg, vegetable oil and sour cream.
Add the wet ingredients to the dry ingredients and stir just until combined. Fold in 3/4 cups of chocolate chips then fill each muffin cup 3/4 full. Top with remaining 1/4 cup chocolate chunks.
Bake the muffins for 18 to 20 minutes or until a toothpick inserted comes out clean. Remove the muffins from the oven, allow them to cool for 5 minutes in the pan then transfer them to a rack to cool completely.