Truffle Macaroni and Cheese

Preheat oven to 350°F and butter a 3-4 quart gratin dish or other shallow baking dish.

In saucepan melt 6 tablespoons butter over moderately low heat. Add flour and cook roux, whisking, 3 minutes. Add milk whisking and bring to a boil. Add mustard, and salt and pepper to taste and simmer sauce until thickened, about 2 minutes.

In a pot of salted boiling water cook macaroni until just al dente, about 7 minutes, and drain well. In a large bowl stir together macaroni, sauce, Cheddar, 1 cup Parmesan, truffle oil and paste transfer to prepared dish.

Sprinkle with remaining Parmesan evenly over macaroni. Cut remaining 1-tablespoon butter into bits and scatter over topping.

Bake macaroni in middle of oven 25 to 30 minutes, or until golden and bubbling.