Preheat oven to 400°F. Grease a standard 12-cup muffin tin or line with paper liners.
In a large bowl, whisk together flour, cornmeal, baking powder and salt.
In a medium bowl, whisk together buttermilk, brown sugar, melted butter and egg.
Add the buttermilk mixture to the flour mixture; stir just until combined (do not over-mix). The batter will still be slightly lumpy, which is fine.
Divide the batter evenly between the prepared muffin cups.
Bake until the edges are golden brown and a toothpick inserted in the center of a muffin comes out clean, about 15 minutes.