Preheat oven to 350F. Spray two 12-count mini muffin pans with floured cooking spray; set aside.

In the bowl of a stand mixer fitted with the paddle attachment (or large bowl and hand mixer), combine egg, butter, sugars, vanilla, and beat on medium-high speed to cream ingredients until light and fluffy, about 3 minutes.

Stop, scrape down the sides of the bowl, and add the buttermilk. Beat momentarily to incorporate.

Add the remaining dry ingredients and mix on low speed until just incorporated; don’t overmix. Batter will be fairly thick.

Using a spoon sprayed with cooking spray so the batter slides off easily, drop rounded tablespoons into prepared pans. Fill each cavity about 2/3 to 3/4-full. I recommend dividing batter equally among the 24 wells.

Bake for 10 to 15 minutes, or until muffins are domed with set centers, springy to the touch, and a toothpick inserted in the center comes out clean.

Allow muffins to cool in the pans for about 10 minutes before removing. While the muffins cool, prepare the topping.

In a small microwave-safe bowl, melt the butter, about 1 minute on high power; set aside.

In a separate small bowl, stir together the sugar and cinnamon; set aside.

After the muffins have cooled, dip the top of each muffin briefly in melted butter, then in cinnamon-sugar, and repeat until all muffins have been coated. Serve immediately.