Preheat oven to 425°F Line a jumbo muffin pan or a 12 cup muffin tin with muffin liners.
In a medium bowl, sift together flour, cinnamon, baking powder, and salt. Set aside. In a small bowl, mix brown sugar, cinnamon and melted butter with a fork. It should be wet and resemble cinnamon roll filling. Set aside.
Using a mixer, beat the butter, brown sugar, and white sugar. Beat for 2 minutes until butter is light and fluffy. Scrape the bowl and add the vanilla. Add in the eggs one at a time. Scrape the bowl between each egg addition.
Add in ⅓ of the dry ingredients and half of the buttermilk. Mix until starting to combine. Add in the next ⅓ of the dry ingredients and the rest of the buttermilk. Mix until combined. Add in the rest of the dry ingredients and sour cream. Scrape the bowl and mix for 10-15 seconds.
Add in half of the cinnamon roll filling into the batter and use a rubber spatula to gently fold in the filling. Use an ice cream scoop for easy pouring to fill the muffin tins ¾th full. Sprinkle a little bit of the cinnamon roll topping on top of each muffin.
Bake at 425°F for 10 mins with a jumbo pan and 8 minutes with a 12 cup muffin pan. Turn the heat down to 375°F and bake for 10-12 minutes for jumbo pan and 6-8 minutes with the 12 cup muffin pan. The muffins are done baking when a toothpick inserted comes out clean.
Let muffins sit in the pan for 10 minutes before transferring to a cooling rack. Allow muffins to cool completely before making the glaze.