Preheat oven to 375 degrees. Spray a 13 x 9-inch baking pan with cooking spray and set aside.

Place the sliced potatoes in a large saucepan and fill to cover with water. Add 1 tablespoon salt. Bring to a boil and cook 5-7 minutes or until you can easily pierce the potatoes with a knife, being careful to not overcook. Drain in a colander and rinse with cold water to cool.

Meanwhile, place the bacon in a large saute pan and cook 5-7 minutes over medium-high heat until crisp. Transfer to a paper towel-lined plate. Reserve 2 tablespoons of the bacon drippings and discard any dark, overcooked bits.

Add 2 tablespoons butter to the bacon drippings and add the onion. Cook over medium heat until beginning to soften, approximately 4-5 minutes.

Add the cabbage and continue cooking another 4-5 minutes or until cabbage is softened. Remove from the heat.

In the large saucepan you cooked the potatoes in, melt the remaining 2 tablespoons butter over medium heat.

Add the flour and cook 1-2 minutes. Slowly add the milk or milk and half-and-half, whisking constantly. Bring to a simmer and cook 3-5 minutes or until thickened. (It won't be terribly thick--the cheese will thicken it some more.)

Add the cheese and whisk constantly until the cheese is melted. Remove from the heat. Stir in the dry mustard and sour cream. Add to the pan the cabbage is in and stir to combine. Add salt and black pepper to taste along with the bacon.

Begin layering as follows:
--1/3 of the cabbage mixture
--Half the potatoes
--1/3 of the cabbage mixture
--Remaining potatoes
--Remaining cabbage

Top with crumbled french-fried onions.

Cover with aluminum foil and bake 40-45 minutes. Remove the foil and continue baking until bubbling and heated through approximately another 15 minutes.

Garnish with chopped fresh chives.