Grease a baking tin well with butter or oil (mine is just a little larger than 8 x 8 inches).
When the dough is ready, divide it into two.
Roll out the first half into a rough rectangle/square shape and place in the prepared tin.
With your fingers, push and ease the dough towards the corners. It will fight you a little and pull back (this is a GOOD sign), but continue until it starts to stay in place.
Melt your butter and spread around ¾ of it over the dough in the baking tin.
Slice your onions finely and place all over the butter (retain several slices to place on the top of the bread and also a little butter).
Sprinkle with as little or as much cheese as you like.
Take the second half of the dough and roll out into the shape of your tin. You will need to roll this one a little more as you are not able to just push it into shape in the pan.
Place on top and gently smooth to the edges until it totally covers the bottom half. Pinch the edges a little so that the top attaches to the bottom half.
Spread over the butter you have left and arrange the remaining onion slices. Sprinkle liberally with sea salt.
Cover with a tea-towel or cloth and leave in a warm place for around 30 minutes. Pre-heat the oven to 200ºC (400ºF).
Bake until the bread is beautifully brown (around 20-30 minutes depending on the size of your tin).
Remove from the oven and allow to cool for a while. Remove from the pan, slice and serve warm with your favourite soup. Enjoy!