01 -
Take the hot pan out of the oven and let it chill for about 10 minutes. Things will thicken up while it sits. Grab some plates and dig in while it’s warm.
02 -
Pop foil over the pan and let it bake for an hour. Then take the foil off and give it another half hour so the top gets bubbly and golden, and the potatoes go soft.
03 -
Lay down half the potato slices in the dish, then toss on half the onions, cheese, bacon, and pour half your creamy sauce over. Go back and do another layer with everything that’s left, making sure to finish up with cheese right on top.
04 -
Get a new saucepan and melt the butter on medium. Shake in the flour and keep whisking to make a thick paste for about two minutes so you don’t taste raw flour. Pour in the milk a bit at a time and whisk until it thickens, a couple more minutes. Add a bit of salt and pepper.
05 -
Either fry the bacon in a pan or bake it at 400°F for 15 to 20 minutes until good and crispy. Let it cool down, then break it into chunky bits.
06 -
Heat up the olive oil in your skillet over medium. Dump in the onions with some salt and pepper and cook, stirring now and then for about 20 minutes or so, until they turn a nice deep brown. Move those to a bowl and set aside for later.
07 -
Crank your oven up to 350°F. Smear some butter all over a 9x13 baking dish. If you've got a mandoline for even, super-thin slicing, now's the time to grab it.