Preheat your oven to 400 degrees and line a 12-cup muffin tin with paper liners. Scoop the batter into the cups, filling each cup nearly to the top. Optionally, add coarse sugar and salt to the tops of each muffin before baking. Bake for 12-14 minutes, or until a toothpick comes out with just a few crumbs clinging to it. Repeat with remaining batter. Serve warm with butter.