Pre-heat your oven to 375° and line a muffin pan with paper or silicon liners. If you don't have liners, you can spray the muffin pan thoroughly with non-stick spray.
In a small bowl, mix together the cinnamon and white sugar. Set aside. This will be the cinnamon swirl.
In a large bowl, add your melted butter, milk, eggs, vanilla extract, and brown sugar. Whisk together until combined.
Evenly sprinkle the all purpose flour over the wet ingredients, then the baking powder, baking soda, and salt. Whisk into the wet mixture until thoroughly combined.
Add about 2 tablespoons of batter into each lined muffin cup then sprinkle with about a tablespoon of the cinnamon swirl mixture. You can then take a toothpick or knife and swirl the cinnamon into the batter.
Add the remaining batter over top of the cinnamon swirl mixture. Each muffin should be filled to about ¾ to the top.
Crumble Topping
Mix together the flour, brown and white sugar, and cinnamon. Pour the melted butter into the mixture and mix with a fork until it looked like wet sand and you no longer see white flour.
Top each muffin with about a tablespoon of the crumble. Be sure to use it all!
Bake the muffins in the pre-heated oven for 15-16 minutes. (A toothpick inserted in the center should come out clean)
Optional Glaze
Whisk together the powdered sugar, vanilla, and milk then drizzle over the cooled muffins.