Preheat oven to 350. Spray muffin tins with cooking spray.
In a bowl combine the flour, sugar, baking powder, salt, cheese and onions, stir until well combined. Pour in 1/4 a cup of melted butter plus the 6 oz of beer, stir until just combined.
Pour batter into muffin tins until each well is about 1/2 full. Pour remaining 2 tbs of butter onto the tops of the muffins, dividing evenly between each muffin. Top with additional cheese, if desired.
Bake at 350 for 18-20 minutes or until the muffins have puffed and a toothpick in the center comes out clean. Serve immediately, these are best right out of the oven.