Start by spraying your 9x13-inch dish with cooking spray so nothing sticks later.
Layer half your sliced potatoes on the bottom and sprinkle with salt. That keeps them tasty.
Melt 2 tablespoons butter in a skillet over medium heat, then add your chopped onion. Cook till they’re translucent and smelling sweet.
Toss in your sliced cabbage and let it cook till it's soft and wilted, about 7 minutes, stirring so it’s all even.
Sprinkle your flour over the veggies, stir it in, and cook for a couple minutes. It’s the drill for a good sauce.
Slowly whisk in the milk while stirring. Keep it moving till it thickens, about 3-5 minutes, like a creamy dream.
Remove from heat and mix in half the cheese and crumbled bacon. Spread this mixture evenly over the potatoes.
Top with the rest of the potatoes, sprinkle salt again, dot with the remaining butter, and finish with the rest of the cheese. Cover with foil and pop it in a 375F oven for 30 minutes. Then take off the foil and bake 15 more till the top’s golden and the potatoes have that tender pull you want.