On Wisconsin! Casserole - cooking recipe

Ingredients

1 lb bratwurst, cooked & cooled
1 tablespoon butter
1 tablespoon olive oil
1 large sweet onion, halved, then sliced in julienne strips
8 ounces penne pasta
3 tablespoons butter
3 tablespoons flour
2 (12 ounce) bottles beer, I recommend a craft beer, I used pale ale (room temperature)
4 ounces sharp cheddar cheese, shredded
2 ounces swiss cheese, shredded
fresh ground pepper
1 tablespoon mustard, stone ground or spicy brown
1/4 cup French-fried onions

Preparation

Bring a large pot of salted water to a boil for pasta. Cook pasta until l dente, drain.
While boiling water & cooking pasta, melt 1T butter & 1T olive oil together over medium high heat. Add onions & a pinch of salt. Caramelize until very golden & soft. Add to large bowl.
Slice brats while onions carmelize, add to large bowl.
In same pan as onions, melt 3T butter, add flour to make a roux, cook 1 minutes. Gently stir in 2 cups of beer, continue stirring until roux dissolves, bring to a simmer & cook 1-2 minutes until thickened & flour taste cooks out. Recede heat, gradually add cheeses stirring until melted & smooth. Add mustard & pepper to taste. Stir in extra beer as needed to thin sauce, should be a medium consistency, thin enough to pour smoothly, not thick & gloppy.
Stir drained pasta in with brats & onions, add most of sauce & toss to coat. Pour into a casserole dish, top with remaining sauce. Can be refrigerated @ this point to bake off later.
If refrigerated, warm on counter for an hour before baking.
Bake in a preheated 375* F oven, covered 20 minutes, uncover, top with French fried onions & bake another 10-15 minutes until golden & bubbly.