Food Network teaches how to crush, slice and mince garlic. Peel off some of the papery skin from the garlic and then smash the head of garlic with the heel of your hand to loosen the cloves; if you only need a few cloves, leave the head intact and pull some off. Separate the cloves. To peel a clove, cut away the root end with your knife. Lay the flat side of the knife over the clove while holding the knife handle, then with the heel of your free hand carefully whack the knife against the garlic to separate the skin from the clove. To crush the peeled garlic, lay the flat side of the knife over the clove and smash it again. To slice peeled garlic, lay the clove flat on the cutting board and hold it with the fingertips of one hand, keeping them curled under. Using a rocking motion with the knife, make thin slices by moving the knife slowly across the clove. To mince peeled garlic, lay the flat side of a knife over the clove and smash it. Roughly chop the clove then move your free hand flat across the tip of the knife and use a rocking motion to chop the garlic until it’s finely minced.
Heat the butter and 2 tablespoons of olive oil in a large (12-inch) saute pan, add the mushrooms, and cook over medium heat for 3 to 5 minutes, until they are tender. Add the sherry and continue to saute for a few more minutes, until the sherry is absorbed. Set aside.
Bring a large pot of water to a boil and add a splash of olive oil and a pinch of salt. Add the pasta and cook for 6 to 8 minutes, until al dente. Drain well.
Meanwhile, melt the truffle butter in a large (4-quart) saucepan and whisk in the flour. Cook for 2 minutes over low heat, stirring constantly with a whisk. Slowly whisk in the hot milk and cook for 2 minutes, stirring constantly with a wooden spoon, until the white sauce is thickened and creamy. Off the heat, add the Gruyere, Cheddar, 1 1/2 tablespoons salt, the pepper, and nutmeg.
Combine the pasta, sauce, and mushrooms in a large bowl and pour them into a 10 by 13 by 2-inch baking dish.
Place the garlic and parsley in the bowl of a food processor fitted with the steel blade and pulse until they're minced. Add the bread crumbs and pulse to combine. Sprinkle the crumbs over the pasta and bake for 35 to 45 minutes, until the sauce is bubbly and the crumbs are golden brown. Serve hot.