Whatever Wednesday: Main Dish Mac and Cheese

Working from two different mac and cheese recipes (a Martha Stewart one and a Rachael Ray one), I came up with this dish that wowed the 6-year-old in the house enough to make him eat mac and cheese that didn't come from a box (and to look forward to leftovers):

3/4-1 pound short pasta, cooked
1/4-1/3 pound bacon, cooked and chopped
4 Tbsp butter
1 small onion, finely chopped
1-2 cloves garlic, chopped
3 Tbsp flour
2 1/2 c milk
2-3 c shredded melting cheese, a combination of your favorites - sharp cheddar, gruyere, monterey jack, mozzarella, muenster
Dollop of prepared mustard, preferably Dijon (optional)
Pinch of nutmeg (optional)
1 c breadcrumbs (I like panko)
1/2 c grated Parmesan cheese

Melt butter in large skillet.  Add onion and saute until tender and translucent; add garlic and cook until fragrant, 1-2 minutes.  Stir in flour and cook for 1-2 minutes before whisking in milk.  Stir constantly until thickened and bubbly.  Stir in melting cheeses and turn off heat.  Whisk until smooth.  Add mustard and nutmeg, if using. Add cooked pasta and bacon, pour into greased 9"x13" dish.  Sprinkle with breadcrumbs and Parmesan.  Stick under the broiler for just long enough to brown bread crumbs and get sauce bubbly, 5-10 minutes (check frequently to keep from burning top).