Spray a baking dish with nonstick cooking spray and set aside.
Wash the potatoes and prick each with a fork a couple times, then microwave them all on a plate for about 8-10 minutes, or until they are fork tender.
Add the microwaved potatoes to the baking dish and use a potato masher to mash into approximately 1/2" thick pieces. Melt the butter and oil, drizzle over the smashed potatoes, and sprinkle the garlic salt over the top.
Bake in a preheated oven for 30 minutes, or until the potatoes are golden. Add the cheese and bacon and bake for another 10 minutes, or until the cheese is melted and the bacon is a little crisp. Enjoy!
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Notes
Make-ahead tips: cook, smash, and season the potatoes, then cover and store them in the baking dish in the fridge overnight. The next day, pull it out to room temperature while you preheat the oven and then bake as directed.