I added chocolate chips, 1 tsp vanilla, 1/2 tsp nutmeg, & a random amount of cinnamon to the batter. I just sprinkled cinnamon into the mix until the batter tasted good, honestly, haha. For the crumbly part, I cheated. I had some of the crumb mix from a crumb cake box mix leftover, so I just put generous heaps of that on top of each muffin.
They took a few more minutes to bake than the recipe said they would, but the wait was worth it -- these are SO good! Moist, melt in your mouth, cinnamon-y goodness. Here's what they look like: