Cheesehead Mac n' Cheese

4 tablespoons butter
1/2 cup finely diced onion
2 cloves garlic, minced
4 tablespoons flour
1 bottle (12 ounces) beer
2 1/2 cups milk
5 cups shredded cheddar cheese, divided
1 tablespoon Dijon mustard
1 teaspoon garlic salt
1/4 teaspoon black pepper
2 dashes hot sauce
1 box (16 ounces) elbow macaroni, cooked al dente
1 pound of bacon, cooked and crumbled (optional)
1/4 cup grated Parmesan cheese
1 cup crushed pretzels or 1/2 cup seaas a resultned Italian breadcrumbs

Melt butter in a large non-stick pan. Cook onion in butter over medium heat until as a resultft. Add garlic and cook another 30 seconds. Whisk in flour, stirring for a minute or two until well combined. Add beer and milk, whisking constantly. Bring to a boil. When it starts to thicken, turn down heat. Add mustard, garlic salt, pepper and 3 cups of cheese a handful at a time. Whisk until cheese is melted. Add hot sauce.

Remove from heat and stir in macaroni and bacon. Spoon into a 9 x 13 inch casserole dish that has been sprayed with cooking spray. Top with remaining 2 cups of cheddar cheese and the the Parmesan and pretzels. Bake in a preheated 350 degree oven for 35 to 45 minutes or until bubbly and golden.