Banana Muffins with a Brown sugar topping

I made these for the kids for breakfast and they gobbled them up so fast they didn't even last a day! 12 muffins!

1 1/2 cups all purpose flour, plus 2 Tbsp for topping
1 tsp baking soda
1/4 tsp salt
1/2 tsp cinnamon , plus 1/4 tsp for topping
4 very ripe bananas, mashed
2 Tbsp melted butter, plus 1 Tbsp chilled butter for topping
1/2 cup dark brown sugar plus 1/4 cup for the topping
2 egg whites
2 tsp vanilla
1/4 cup nonfat Greek yogurt, plain or vanilla (I used plain)
2 2/1 Tbsp skim milk


Preheat oven to 350. Spray 12 muffin cups with cooking spray. (you could use cupcake liners instead) Mix 1 1/2 cups flour, baking soda, and salt. In a separate bowl, mix bananas, 1/2 cup brown sugar, vanilla, 1/2 tsp cinnamon, egg whites, melted butter. Combine with flour mixture. Add milk. Fill muffin cups about 2/3 full. In a bowl, mix remaining brown sugar, cinnamon, and flour. You could add 1/4 cup of chopped walnuts with this as well. Cut in butter. When crumbly, sprinkle over muffins. Bake for 20 minutes.