Step 1If baking the mac and cheese, heat the oven to 400 degrees and butter a 13- by 9-inch baking or casserole dish.
Step 2Meanwhile, bring a large pot of salted water to a boil. Add the macaroni to the water and cook until it is just al dente, stirring occasionally to keep the noodles from sticking together and to the bottom of the pot. Drain the macaroni in a colander, then place into a large bowl and set aside.
Step 3In a large saucepan, melt the butter over medium-high heat. When it’s melted, quickly whisk in the flour to keep it from clumping and to form a roux. Reduce the heat and continue to cook the roux, whisking constantly, for two minutes.
Step 4Slowly pour in the milk while whisking. Add the pepper and bay leaves. Increase the temperature until the mixture begins to simmer, still whisking, and cook until it thickens to the consistency of heavy cream. Remove from heat and fish out the bay leaves, using a pair of tongs or spoon.
Step 5Gradually add the Gruyère and cheddar cheeses, along with 1 cup of Parmesan to the sauce, stirring until the cheese is melted. If the sauce is too thick, whisk in additional milk, a tablespoon or so at a time. When the cheese sauce is smooth, pour it over the bowl of pasta and stir until combined. Serve if desired.
Step 6To bake the mac and cheese, spoon the mixture into the baking dish. In a small bowl, combine the bread crumbs with the remaining Parmesan cheese and sprinkle the mixture over the pasta. Bake until the bread crumbs are golden brown and the mac and cheese is bubbly, about 25 to 30 minutes.