Preheat oven to 375 F. In a small saucepan melt 21/2 tablespoons butter over low heat. Remove from heat and add panko and Parmigiano-Reggiano. Toss to combine, and set aside.

Add 1 ½ scant teaspoons kosher salt to 2 quarts water, and bring to boil in a large saucepan.

Put the remaining 3 tablespoons butter in a 2-quart, heavy-bottom saucepan and melt over low heat. Add flour and cook for about 3 or 4 minutes over low heat, whisking constantly. Add milk and cook for 5 minutes, whisking or stirring with a wooden spoon constantly.

Remove from heat and add remaining 1 ½ teaspoons kosher salt, 5 to 6 grinds of pepper, nutmeg and cheeses. Stir until the cheese is melted. If the cheese doesn't melt completely, return mixture to very low heat and stir constantly until melted; then remove from heat.

Cook the macaroni in salted water until al dente, about 6 minutes, or according to package directions. Drain thoroughly and combine with cheese sauce, mixing with a wooden spoon. Add peas and prosciutto.

Pour macaroni mixture into a 2-quart baking dish. Sprinkle the reserved bread-crumb mixture evenly over the top of the macaroni and cheese. Bake 30 to 45 minutes, or until browned and bubbly. If after 35 minutes it's not yet done, turn up heat to 400 F. Makes 4 to 6 servings.

To make ahead: Put macaroni and cheese in the baking dish, cover and refrigerate until ready to bake. Bring to room temperature before baking, and be prepared for it to take a little longer to heat through.

Note: If not using fresh nutmeg, use just a pinch of preground nutmeg.

PER SERVING (BASED ON 5 SERVINGS): Calories 741 (50% fat) Fat 42 g (25 g sat) Cholesterol 134 mg Sodium 1,880 mg Fiber 3 g Carbohydrates 53 g Protein 40 g

SOURCES: Adapted from an Ina Garten recipe on foodnetwork.com and a Terrance Brennan recipe on msnbc.com