1 tablespoon olive or vegetable oil
12 slices of meaty bacon, divided
2 large onions, quartered and thinly sliced
Salt and coarse black pepper
1 tablespoon Worcestershire sauce
1 tablespoon light brown sugar
1 cup stout beer
For the base sauce:
2 cups heavy cream
1 clove garlic, crushed
1/2 cup grainy mustard
3 cups orange sharp cheddar cheese
1 pound short-cut pasta, cooked for 6 minutes in salted water and drained
For the topping:
2 cups coarse crushed mustard pretzels
4 tablespoons butter
2 cloves garlic, chopped
3 tablespoons Red Hot or other cayenne pepper sauce
1 cup grated Parm cheese
1/4 cup chopped flat leaf parsley, finely chopped
Preheat oven to 375°F and bake 8 slices of bacon on wire rack set into a rimmed baking sheet or on slotted broiler pan to crisp.
Finely chop 4 slices bacon and heat skillet with 1 tablespoon oil, 1 turn of the pan. Add bacon and render 2 minutes. Add onions, season with salt and pepper, and cook over moderate heat until very tender, 12-15 minutes. Add Worcestershire, light brown sugar and beer, and simmer a minute more.
Make the base sauce for the mac: Bring cream, garlic clove and mustard to a low boil and simmer 5 minutes to thicken. Remove garlic clove and add in cheese; stir to melt.
Combine bacon and onions with sauce and pasta, and place everything in a casserole dish.
Place pretzel crumbs in bowl. In a small pot, melt butter over medium heat with garlic, swirl a minute or so, then add hot sauce and swirl to mix. Pour over pretzels, toss with cheese and parsley, and sprinkle over the casserole.
Bake to bubbly and brown, and serve.