Classic Streusel Topping

1. Preheat oven to 350 degrees F (175 degrees C). Coat muffin pans with non-stick spray, or use paper liners. In a large bowl, sift together the flour, baking powder, baking soda, salt and cinnamon and set aside.
2. In the bowl of your stand mixer, add bananas and turn on your mixer to use the mixer’s paddle to mash the bananas. Then, add sugar, egg, and melted butter. Slowly fold in the flour mixture, and mix until just combined. Lastly, gently fold in the blueberries and walnuts. Scoop the batter into the muffin pan.
3. Make the streusel topping: In a large bowl, stir together the brown sugar, granulated sugar, all-purpose flour, cinnamon, and salt. Add the pieces of cold butter into the bowl and use a fork to cut the butter into the mixture until it is the texture of coarse meal. (You do not want it to become a cohesive dough). Sprinkle some on top of each muffin. Add a few extra blueberries to the top of each muffin.
4. Bake in preheated oven. Bake for about 21-25 minutes until golden brown and until a toothpick inserted into the muffin comes out clean.
5. Serve warm from the oven or let cool and store in an airtight container in your freezer for up to one month.
6. The night before you want to eat them, place desired amount into a re-sealable plastic bag and leave them on top of your kitchen counter. They will be ready to eat in the morning. If you want them warmed, heat them in your microwave on high for about 20 seconds.