1. In a saute pan on a medium heat with olive oil add the mushrooms, shallot, thyme, salt and pepper. Saute for 5 minutes. Then add the cognac and cook for 1 minute until alcohol is absorbed then remove mushroom mixture from pan and place in a large bowl.
2. In a separate pot add milk and heat until just a boil but not to a boil just hot milk.
3. In a 4 quart pot on low heat, add truffle butter and let melt and slowly whisk in the flour keep whisking for 2 minutes until flour taste is cooked out.
4. Slowly add the hot milk to the butter flour mixture constantly whisking until all the milk has been added. Cook on low for 2 minutes. This bechamel sauce will thicken up but constantly keep whisking the sauce. Add nutmeg, salt and pepper to the bechamel.
5. Turn the bechamel sauce off and immediately combine all the grated cheeses to the bechamel. Stir the sauce and all the cheeses will melt into one thick cheesy sauce.
6. The pasta should be ready and cooked at the same time your bechamel sauce is done. Under cook your pasta by 1 minute because it will cook further in the oven.
7. In one large bowl combine mushrooms, pasta and bechamel. Stir to incorporate.
8. Place olive oil and garlic in a nonstick pan. Bring to a medium heat and cook the garlic for 1 minute. Add the panko, salt and pepper and cook for 2 minutes until slightly browned.
9. Add the mac & cheese to your favorite baking pan top with crunchy browned panko and bake on 375 degrees for 30 minutes until cheese is bubbling and panko is browned.