Preheat an oven to 375 degrees and spray a 12-muffin tin with non-stick spray.
Mix all ingredients in a large bowl and stir to thoroughly combine.
Distribute the muffin batter between the cups. Tap the tin on the counter a few times to get any air bubbles out of the batter. Top each muffin with 1 tsp brown sugar, if desired (this is what forms the brown sugar crunch on top!)
Bake for 27 minutes, or until a toothpick inserted in the center of a muffin comes out clean, typically between 25 and 30 minutes. Serve hot with butter or desired topping!