Preheat oven to 400 degrees F. Spray a standard 12-cup muffin tin with cooking spray or line with paper cups. Set aside.
Combine flour, brown sugar, baking soda, cinnamon, salt, nutmeg and allspice in a large bowl. Use a pastry cutter or two forks to cut cold butter into the dry ingredients until the butter is in tiny pea-sized lumps.
In a separate bowl, whisk together milk, egg and vanilla extract. Stir the milk mixture into the dry ingredients, just until moistened. Batter will still be slightly lumpy, but that’s fine.
Spoon the batter into the prepared muffin tin. Bake for 15-20 minutes, or until a toothpick inserted in the center comes out clean.
In a small bowl, stir together the cinnamon and sugar for the topping. When the muffins are cool enough to handle, brush the tops of the muffins with melted butter, and then sprinkle with the cinnamon-sugar mixture.