Preheat oven to 350˚ Fahrenheit (177°C) with the rack in the middle. Grease a 12 count muffin pan with baking spray. If using muffin liners, spray them first so they don't stick to the liners. This will make 15 muffins, if you have an extra muffin pan handy prep that as well.
In a large bowl whisk together the flour, baking soda, salt and cinnamon. Set aside.
In a separate bowl, whisk together the maple syrup and brown sugar getting out as many lumps as possible. Fold in the mashed banana, sour cream and beaten egg. Add the wet into the dry ingredients and mix to combine. Batter will be thick. Mix in the milk. Fold in the chocolate chips, then carefully the raspberries. Be very gentle with the berries so they don't turn the batter pink. Do not overmix the batter as it will toughen the muffins.
Evenly divide the batter between the muffin tins, filling to the top. Top with more chocolate chips if desired. Bake for 17-18 minutes, until you see light brown edges. A toothpick inserted into the centers should come out virtually crumb-free. If you are using the same pan for the three extra muffins, fill the empty muffin time halfway with water so the muffins bake evenly and your pan doesn't warp.
Let the muffins cool for 10 minutes before removing from the muffin pan. Transfer to a wire rack to cool completely.