Preheat oven to 350F. Butter or line a 12-cup muffin tin. This recipe will make about 9-10 large muffins like the ones in the post, or a dozen slightly smaller ones depending on how much you fill your muffin cups.
Whisk together all the dry ingredients.
In a separate bowl, whisk together all the wet ingredients and the add them to the dry ingredients.
Mix until everything is well incorporated and there are no dry pockets of flour left.
Spoon the batter into your prepared muffin tin. Fill them almost to the top for 9-10 larger muffins, or about 3/4 full for about a dozen medium sized muffins.
For the topping, mix the cinnamon and the granulated sugar together, and sprinkle it on top of the muffins, along with the oats, if desired.
Bake for 20-25 minutes until risen and starting to turn golden around the edges.
Remove from the oven and allow to cool partially in the pan before removing to a baking rack to cool completely.