Fill a large pan with 3 inches of water and bring it to a boil on the stove. Boil the Bratwurst (6) for about 15 minutes to let them plump up and cook through. Remove them from the pan and drain the water, then get it back on the medium-high heat.
Sear the bratwurst for a couple of minutes in the hot pan to get some color on the outside. Then set them aside on a cutting board.
Combine the Butter (6 tablespoon) and All-Purpose Flour (6 tablespoon) in the hot pan and stir it together until it becomes a thick, golden roux. It should take no more than two minutes.
Pour the Beer (1 cup) in and let it bubble for about 30 seconds as you stir. Switch to a whisk and slowly pour the Milk (3 cup) in as you whisk to get a smooth white sauce going. Season it with the Truffle Salt (1 pinch). Let the sauce gently bubble and boil for about 15 minutes to thicken, whisking occasionally so it doesn't burn.
While the sauce cooks, get a large pot of water on the stove to boil for the pasta. Salt it generously. When it's boiling, cook the Medium Pasta Shells (1 pound) until tender, 8-10 minutes. Slice the cooked bratwurst into little rounds to make them bite-sized.
Once the bechamel sauce has cooked for 15 minutes, whisk in Sharp Cheddar Cheese (1 cup), Smoked Gruyere Cheese (1/2 cup), and Smoked Gouda (1/2 cup) until it becomes a smooth, rich sauce. Stir in the sliced bratwurst as well and let the mixture bubble together for a minute.
Drain the pasta shells and add them to the pan with the cheese sauce and bratwurst. Stir it all together well, then take the pan off of the heat.
Serve immediately and enjoy!