Cook pasta in salted, boiling water until tender but not mushy.
While the pasta cooks, cook the bacon and onions together until the bacon is crisp and the onion is tender.
Remove from pan and set aside.
Pour off all but about 2 tablespoons of grease from the pan.
Add the hamburger, sprinkle with salt and pepper and cook it thoroughly.
Add the bacon and onions back to the pan, along with the butter.
Stir until butter is melted and sprinkle with the flour.
Cook for 2 minutes, stirring.
Stir in the well-drained pasta.
Whisk the eggs and mustard into the milk and pour over the meat mixture.
Add the grated cheese.
Cook, stirring constantly until thickened and well blended - about 3 minutes.
Notes
Storage:Cover and refrigerate 4 to 5 days. Freezes well for up to 6 monthsTips:
Don't pour bacon grease down your drain—too many times doing so and you can get a clog! Instead, line a bowl with a bag or some foil and pour it in there. Let it cool, then wrap it up and store or toss!
You can use a meat chopper to break down the ground beef in your pan more evenly.
Shred cheese from a block if you want it to be extra smooth and delicious. Pre-shredded cheese has a coating to prevent it from sticking together.