Put the bread on the rack of a grill pan and put the pan under a hot grill so both sides are lightly toasted.
2
Spread one side of each slice of toast with butter and then add as much mustard to taste. Top with cheese.
3
Put under the hot grill until the cheese is soft and bubbling and beginning to turn golden brown.
4
Sprinkle with a little black pepper and paprika or cayenne and serve immediately.
Mix it up: As an alternative method, use up leftover cheeses in the fridge, grated and stirred together with the butter and mustard before spreading it on toast and grilling.