Ingredients
1 tbsp mayonnaise
Freshly ground pepper
80g cheese, finely grated - whichever takes your fancy but cheddar works particularly well
½ onion, finely sliced
Salt to taste
4 slices of bread (I really like my toasties to be with white sandwich bread)
50g butter
1 tsp flavourless oil

Method
If you want to add a thin layer of butter inside do, it makes it buttery oozy and lovely but this step is optional.

Spread a little of the mayonnaise over each slice of bread, this just helps to stick your filling in place.  Put some freshly ground black pepper over 2 of the slices.  Put the sliced onion down on to two slices of bread and top with the cheese and a little sprinkle of salt.

Put the tops on the sandwiches and butter the very top slice on the outside.

Take your frying pan and put in ½ tsp of the oil and turn the heat to medium - the oil stops the butter from burning.  Put the sandwiches into the pan, butter down.  Whilst the sandwich is in the pan, carefully butter the top slice taking care as the pan will now be hot.  Cook for 3-5 minutes until the bottom is golden.

Very carefully turn over and add the remaining ½ tsp of oil if needed and continue cooking until the bottom is also golden.  Your cheese should be melted and both sides golden. 

Remove from the pan and cut each sandwich into 2.  Enjoy hot.