Preheat the oven to 350 degrees F. Grease a 12-cup non-stick muffin tin with vegetable oil spray.
Place the cornmeal, flour, sugar, salt and baking powder in a medium bowl and whisk to combine. Stir in the cheese.
Beat the egg in a second medium bowl. Mix in the buttermilk and melted butter. Mix the wet ingredients into the dry until just combined. Spoon the batter into the prepared pan.
Bake for 18 to 20 minutes, or until muffin springs back when gently touched in the centre.
Recipe Options: Instead of old cheddar, try another tangy cheese in these muffins, such as Monterey jack or asiago. For added colour and flavour, mix 2 thinly sliced green onions into the batter before spooning into the muffin tin.