Combine the milk and vinegar in a bowl and leave to sit for a few minutes while you prepare the rest of the ingredients. Combine the polenta, gluten free flour, baking powder, sugar and salt in a mixing bowl. Then add the milk and vinegar,the egg and finally the oil. Whisk gently with a fork and leave the batter to rest for about 10 minutes.
When you are ready, heat a medium frying pan so that it is very hot. Place a small amount of butter or oil in the pan and wait until it is sizzling. Then add a ladle full of batter. Cook until you see the surface has lots of tiny air bubbles, then flip over and cook for a few seconds on the other side. Serve immediately with more butter and maple syrup.
It's best to use a combination of butter and oil for greasing the pan. The oil allows you to heat your pan to a high temperature without burning and the butter adds a wonderful flavour.
And here's a little tip I learned from Richard Bertinet. Apparently this is how they make those famous Breton Crepes. Cut a small potato in half. Pierce the non-flat side with a fork. Dip the flat side in the butter and oil mixture and then use this to grease the pan. It works magnificently!