Preheat oven to 400°F Butter ten to twelve 10-oz. ovenproof bowls or ramekins; set aside.
Bring a large pot of water with 1 tablespoon of salt to boiling. Add pasta, stir just until water returns to boiling. Cook pasta according to package directions just until tender to the bite (al dente). Drain, shaking well. Meanwhile, in a mixing bowl beat egg whites with electric mixer to stiff peaks.
In Dutch oven, melt butter over medium-low heat. Add onion and cook until softened. Sprinkle the flour over onion; stir constantly for 2 minutes (do no allow flour to brown). A little at a time, add 1 cup of the milk, stirring constantly until smooth.
For an herb bundle, in an 8-inch square double-thickness of cheesecloth, place the bay leaf, thyme, and peppercorns. Gather corners and tie with 100% cotton string. Add herb bundle to Dutch oven 1 to 2 teaspoons of salt and remaining 2 1/2 cups of milk. Increase heat to medium-high and bring to boiling, stirring frequently (do not let the mixture boil over). Boil for 1 minute; reduce heat to low so milk barely simmers. Cook, stirring frequently, for 10 minutes more. Remove from heat; let stand for 5 minutes. Remove and discard herb bundle. Immediately stir in plenty of ground blackpepper, the nutmeg, and the cheeses. Stir just until cheeses are melted.
Stir cooked macaroni into cheese mixture. Fold in beaten egg whites. Spoon mac and cheese into prepared bowls. Top with Garlic Bread Crumbs.
Bake for 15 minutes or until heated through (160°F) and crumbs are toasted. To serve, top with truffle oil and fresh thyme.
*Garlic Bread Crumbs: In a food processor, process 5 oz. (3 thick slices) country-style white bread, crusts removed, to coarse crumbs. Transfer to a bowl. Toss with 2 cloves garlic, minced; 1/2 teaspoons salt; and 1/4 teaspoons freshly ground black pepper. Add 2 1/2 tablespoons olive oil. With a rubber spatula, work oil into the crumbs.