Layer 2 slices of fontina cheese between 2 slices of white bread and shave a couple of slices of truffles in the middle of each sandwich; do the same for all four sandwiches.
Heat a large frying pan over medium heat and add the butter.
When the butter melts, add the sandwiches and cook until the bread is nice and toasted.
Remove and slice sandwiches in half and place onto four plates.
Wild arugula salad: Place arugula in a small bowl with the vinegar, extra-virgin olive oil, sliced shallots, and season with salt and pepper.
Toss the salad well and garnish the plates with it.