For the truffle spread: Thoroughly combine the robiola, lemon zest, rosemary, truffle oil and some salt and pepper in a bowl. Reserve at room temperature.
For the mushrooms: Heat 1 tablespoon of the olive oil in a large, heavy skillet over medium-high heat until it shimmers. Add just enough of the mushrooms to loosely cover the bottom of the skillet (you should be able to see the pan between the mushrooms). Season the mushrooms with salt and pepper. Cook for about 2 minutes, then gently turn the mushrooms over as they brown and soften.
Add a little chopped shallot and garlic, some butter and some rosemary and thyme to the pan. Continue cooking until the mushrooms are tender, about 2 minutes more; transfer to a paper towel.
Wipe out the skillet and repeat the process, cooking the mushrooms in small batches. Reserve at room temperature.
For the grilled cheese: Preheat a griddle over moderately low heat to 350 degrees F.
Brush one side of each bread slice with softened butter. Spread the opposite side with truffle spread (1/4 cup per slice). Top each with a slice of fontina and a slice of Gruyere Spoon 1/2 cup of the mushrooms onto each slice. Sprinkle with the herbs and season with salt. Close the sandwiches.
Set the sandwiches on the hot griddle and press with a large baking sheet weighted down with cans. Cook until toasted, 3 minutes per side.
Cut the sandwiches in half diagonally and serve hot.
Pair the sandwich with smoky tomato soup, for dipping.
This recipe was provided by a chef, restaurant or culinary professional. It has not been tested for home use.