Preheat oven to 350 degrees. Cook pasta according to package directions.

While pasta cooks, sauté mushrooms in ½ cup beer in a large non-stick skillet. When liquid has evaporated and one side is red-brown, flip mushrooms and cook until other side is same color, about 20 minutes.

Melt butter in a large sauce pan and stir in flour. Cook for a minute or two to slightly toast flour. Stir in mustard and salt, then whisk in milk and remaining beer. Bring to a low boil over medium-high heat, stirring occasionally to slightly thicken sauce, for about five minutes. Remove from heat, whisk in cheese and stir to melt. Stir in mushrooms and pasta and transfer to flameproof skillet or Dutch oven. Sprinkle with breadcrumbs.

Place skillet or Dutch oven on baking sheet and bake until cheese bubbles around edges, about 30 minutes. If desired, remove from oven, cover and transport to tailgate, wrapped in blanket or large towel. Reheat on a grill or serve slightly warm.