Banana Crumb Muffins

I found this recipe on allrecipes.com, but made some alterations based on some of the reviewer suggestions. I'm listing the recipe as I made it:

MUFFINS:
1 cup all-purpose flour
1/2 cup whole wheat flour (can make muffins with just 1-1/2 cups regular flour)
1 tsp baking soda
1 tsp baking powder
1/2 tsp salt
1/2 tsp nutmeg
3/4 tsp cinnamon
3 ripe bananas, mashed
1/2 cup granulated sugar
1/4 cup packed brown sugar
1 egg, lightly beaten
1/3 cup vegetable oil
1 tsp vanilla extract
TOPPING:
1/3 cup packed brown sugar
2 tbsp all-purpose flour
1/4 tsp ground cinnamon
1 tbsp cold butter

Preheat oven to 375 degrees. Lightly grease 12 regular-size muffin cups or line with muffin papers.

In a large bowl, mix together flour, baking soda, baking powder, salt, nutmeg and cinnamon. In another bowl, beat together bananas, sugar, egg, oil and vanilla. Stir the banana mixture into the flour mixture just until moistened. Spoon batter into prepared muffin cups.

In a small bowl, mix together brown sugar, 2 tbsp flour and cinnamon. Cut in butter with a pastry blender or two forks until mixture resembles course crumbs. Sprinkle topping over muffins and pat lightly.

Bake in preheated oven for 18-20 minutes or until a toothpick inserted into center of a muffin comes out clean.