Preheat the oven to 180C/160C Fan/Gas 4.
Lightly toast the bread on both sides.
Put the bread on a tray. Use a very sharp knife to carefully cut a shallow well into the centre of the bread, about a 5cm/2in square. To do this cut the edges and push down the centre. Remember this is a well not a hole. It is important that you don’t cut all the way through!
Distribute the fontina evenly around the rim of the well.
Mix the yolks together with the truffle oil and pour them into the well then bake for 3-5 minutes until the cheese melts.
Take the toast out and give the yolk a little stir then sprinkle with salt and pepper. Eat immediately.