Preheat the oven to 170C Fan / 180C / Gas Mark 3. Grease a 12 hole Muffin tin, or use paper cases.
In a mixing bowl, mix the flour, salt, backing powder, bicarbonate of soda, cayenne pepper and onion salt. Add the grated cheese and cooked bacon and mix well.
Melt the butter
In a separate bowl beat the eggs and oil. Add the melted butter and milk and stir.
Add the wet ingredients into the mixing bowl, and fold in.
Divide the mixture into the muffin tin.
Bake in the preheated oven for 20-22 minutes. The muffins should be firm to the touch and golden brown.