In a large bowl combine all of the crumb topping ingredients.
Use a pastry cutter until mixture is crumbly. Set aside.
In a large bowl, cream together butter, brown sugar and white sugar.
Beat in eggs and vanilla extract. Seat aside.
In a medium bowl, whisk or sift flour, baking soda, baking powder, salt, and cinnamon.
Gradually add flour mixture into the wet mixture alternating with the buttermilk.
Stir just until combined. (be careful not to overdo it.)
Add lemon juice to mashed bananas.
Gently fold bananas into the batter.
Fill muffin pan 3/4 full of batter.
Spoon on enough crumb topping to completely cover the top. (pinch the crumbs together to create larger crumbs if desired. I used a little over 1 T. of topping)
Bake for 18-20 minutes.
Remove from oven when moist crumbs cling to a toothpick inserted into the center.
Let muffins sit in the pan for about 4 minutes (they will continue to cook)
Place muffins on a cooling rack to finish cooling.
* The streusel crumb topping makes a lot! Half the recipe if you don't want leftover streusel. I always make the full amount so that I can skip this step when I make future crumb muffins or crisps. Really come in handy *Store muffins in an airtight container. Banana bread naturally gets a moist and sticky surface as it sits. If you are serving this for an event and want the topping to remaining crunchy, I'd suggest making this the day of.