Heat your oven to 400°F. Get this going first so you’re not standing around waiting later.
Cook the bacon in your skillet (cast iron if you have it, whatever works if you don’t) until it’s crispy. Take it out and set it aside on paper towels. Don’t clean the pan – you want all that flavor.
Cook the beef in the same pan with all those bacon drippings. Break it up as it cooks and season with the mustard powder, paprika, garlic powder, salt, pepper, and Worcestershire sauce. Cook until it’s no longer pink.
Layer everything up: Push the beef to one side and start layering – some potatoes on the bottom, then beef, then more potatoes, then the rest of the beef, then finish with potatoes on top. Don’t stress about making it perfect.
Add the milk and cheese – pour the milk over everything and sprinkle the cheese on top.
Bake for about 45 minutes or until the potatoes are tender and the cheese is golden and bubbly. If there’s still a lot of liquid sloshing around, give it another 10-15 minutes.
Let it cool for a few minutes (seriously, it’ll be molten lava hot), then sprinkle with the crispy bacon pieces and green onions if you’ve got them.