Preheat oven to 375 degrees. Butter a 3 quart casserole dish and set aside. Tear bread into 1/2 inch pieces. Place in medium bowl and add 2 tbsp. melted butter. Toss with bread and set aside.

In a medium saucepan over medium heat, warm up the milk. Melt the remaining butter in a large, high-sided skillet over medium heat. When the butter bubbles, add the flour. Cook the flour and butter, whisking constantly, for 1 minute. While whisking the flour, add the hot milk, a little at a time to make the mixture smooth. Continue to mix and cook, whisking constantly until the mixture begins to bubble and thicken, approximately 10-12 minutes. This may take a little longer, but be patient.

Remove the pan from the heat and stir in the salt, black pepper, cayenne pepper, nutmeg, 3 cups of cheddar and 1 cup of Gruyere. Mix well and set aside.

Bring a large pot of salted water to a boil. Cook the elbow macaroni for 3 minutes. It will be under-cooked. Drain the pasta and rinse it under cold water to stop the cooking. Add the pasta to the cheese sauce and mix well.

Pour mixture into prepared casserole dish. Sprinkle the remaining Cheddar and Grueyere over top. Add the buttered bread pieces and put them all over the top of the cheese. Bake for 25-30 minutes until golden brown.