Preheat oven to 400ºF. Line muffin tins with liners or spray well with cooking spray and set aside.
For the muffins, in a medium bowl whisk the flour, baking powder, salt, sugar, and graham cracker crumbs until blended. Set aside.
In the bowl of a stand mixer, combine the milk, oil, egg, and vanilla and beat until incorporated. Add the dry ingredients and mix until just combined. Add the chocolate chips and stir in by hand.
Fill each muffin liner or tin about 2/3 full.
For the topping, in a bowl mix the flour, brown sugar, graham cracker crumbs, cinnamon and stir to combine all the dry ingredients well. Add the melted butter and mix well until crumbly and looking like wet sand.
Top each muffin with 1 heaping tablespoon of crumb topping.
Bake for 16-19 minutes or until a toothpick inserted into the middle comes out clean. Makes 12 muffins.