I tend to go for the 'Harry's Bar' Venitian reciepe:

Ingredients

250g Fontina, or Gruyère, or other melting cheese
1 tbsp Dijon mustard
2 tbsp Worcestershire sauce
1 dried red chilli or ¼ teaspoon cayenne pepper
1 egg yolk
3 tbsp double cream
Sea salt
12 slices sourdough bread
6 slices prosciutto
Olive oil


▶ Cut the cheese into small dice and put into a bowl in a warm place for 30 minutes. Mix the mustard with the Worcestershire sauce, and add the chilli or cayenne and the egg yolk. Put the cheese into a food processor and add the cream. Pulse-blend for a few seconds, then stir in the mustard mixture. You should have a smooth thick sauce that will spread easily. Season with sea salt.

▶ Trim the crusts off the bread and spread the cheese mixture over one side of each slice. Lay the prosciutto or speck over six slices and cover with the remaining slices, cheese side down. Press sandwiches together firmly and cut each one into three pieces.

▶ Heat a large frying pan. Pour in enough oil to cover the surface. When the oil is smoking, add as many sandwiches as will fit. Fry for about 3–4 minutes, until light brown and crisp, then turn over and fry the other side. Drain on kitchen paper. Repeat until all the sandwiches are cooked.