• Preheat the oven to 375˚F.

Making the Filling/Topping

• In a medium bowl, combine melted butter, brown sugar, cinnamon, and flour with a fork until well combined. Set aside.
  4 tbsp salted butter, 1/2 cup brown sugar, 2.5 tsp cinnamon, 1/2 cup all-purpose flour

Make the Muffins

• Combine flour, baking powder, baking soda, and salt in a small bowl. Set aside.
  2 cup all-purpose flour, 2 tsp baking powder, 1 tsp baking soda, 1/8 tsp salt
• Using a stand or hand mixer, beat together butter and sugar on medium-high until light and fluffy.
  8 tbsp salted butter, 2/3 cup sugar
• Add the eggs and vanilla and mix until just combined. Do not overmix.
  2 eggs, 1 tsp vanilla extract
• Add half of the flour mixture, then the buttermilk, and the rest of the flour. Beating until just combined, scraping down the sides if needed.
  3/4 cup buttermilk
• Add ~2 tbsp of batter to prepared muffin tins, drop a dollop of the filling on top, and then top the filling with 2 tbsp of batter.
• Add the rest of the topping to the tops of the muffins, gently pressing it into the batter if needed.
• Bake for 20-23 muffins or until the muffins are barely browned on top and a toothpick inserted into the middle comes out clean.

Make the Icing

• Make the icing while the muffins cool (for ~5 minutes) by whisking together powdered sugar, milk/cream, and vanilla extract.
  1/2 cup powdered sugar, sifted, 1 tbsp heavy cream or whole milk, 1/2 tsp vanilla extract
• Drizzle the glaze over the top of the warm (not hot!) muffins.