Step 1

Preheat the oven to 350º F (180º C). Line a muffin pan with cupcake liners.

Step 2

In a large bowl, whisk together the flour, baking powder, baking soda, and pumpkin pie spice. Set aside.

Step 3

In a separate medium bowl, whisk together the melted butter, brown sugar, pumpkin puree, vanilla, buttermilk, and vinegar.

Step 4

Add the wet ingredients to the dry ingredients and mix just until combined. Spoon the batter into liners.

Step 5

Add the sugar, flour, and cinnamon to a medium bowl and stir to combine.

Step 6

Add the butter and use a fork, or pastry cutter, to cut the butter into the flour until the mixture is made of coarse crumbs.

Step 7

Sprinkle the mixture evenly over all of the muffins.

Step 8

Bake for about 25 -30 minutes, or until a toothpick inserted in the center comes out clean. Allow the muffins to cool for 20 minutes in the muffin pan, then transfer to a wire rack to continue cooling.

Step 9

When muffins are cool, whisk together the powdered sugar and milk and drizzle over the tops.