Butter an 8-inch bread pan well. Set aside.
Sift the flour, baking powder, sugar and salt together into a bowl. Whisk in the cheese and the onion.
Whisk together the egg, milk and melted butter.
Add all at once to the dry ingredients and stir together to blend. It will be a thick dough. Do not beat or overmix. (If you think it is too stiff you can add a bit more milk.)
Spread into the prepared pan and leave to sit for 20 minutes.
Preheat the oven to 350C/ gas mark 4. (regular oven not fan)
Bake for 1 hour. It is done when it is golden brown and a toothpick inserted in the center comes out clean.
Tip out of the pan onto a wire rack to cool. This can be served warm or at room temperature, cut into slices and buttered. It also freezes well.
