I believe that this recipe originally came from a Gourmet magazine, which I adapted to simplify. It is rich and very delicious.
1 lb tube shaped pasta such as rigatoni or penne rigate (Campanelle is also very nice)
2 tbsp butter
1 medium yellow onion, peeled and coarsely chopped
1 clove garlic, peeled and minced
1 sprig fresh thyme
1 sprig fresh rosemary (optional)
1/4 cup dry white wine or vermouth
2 tbsp flour
3 1/2 cups milk
2 tbsp Dijon mustard (ideally whole grain)
1 lb aged cheddar cheese grated on large holes of a box grater
1/2 cup coarse bread crumbs (make by putting stale or fresh bread, crust removed, through a food processor)
1. preheat oven to 400. Cook pasta in a large pot of boiling salted water for 5 to 7 minutes — you do not want the pasta to be fully cooked. Drain, then rinse under cold running water in a collander.
2. melt butter in a large saute pan over medium heat (I like to use a cast iron pan so I only have one pot to wash). Add onions, garlic, thyme, and rosemary (if used) and cook until onions are soft, 8-10 minutes. If you do not have fresh herbs, use a pinch of dried thyme. Add wine and cook for 2-3 minutes. Remove and discard the sprigs of herbs (if you used dried herbs, just leave in the mix). Whisk in flour and cook, stirring for 1 minute. Gradually whisk in milk then mustard. Reduce heat to keep the sauce at a gentle simmer and cook, stirring constantly, until thick and creamy (about 30 minutes). Remove pan from heat and stir in most of the cheese, leaving about 1/2 to 1 cup of cheese for the top. Stir in the cheese a handful at a time, stirring until completely melted after each addition. Season to taste with salt and pepper.
3. fold pasta into sauce and stir until well coated. If your pan is not oven-proof, transfer everything to a baking dish. Scatter the remaining cheese on top, then sprinkle with bread crumbs. Bake until crust is golden, about 25 minutes.