Preheat your oven to 325F
Peel and dice your potatoes. You're aiming for about 7ish cups of medium diced potatoes. Wash them off and add to a large pot of salted water.
Parboil the potatoes for about 10 minutes. This means once the water starts to boil, start timing.
After ten minutes, drain well. Do not rinse.
While the potatoes are boiling, grate the cheddar cheese.
In a large bowl, combine the mayonnaise, shredded cheddar cheese, bacon, grated garlic and onion, thyme, salt, and black pepper.
Add the potatoes and stir until evenly coated.
Spray a 9x13 casserole dish with cooking spray.
Add the potatoes and spread into an even layer.
Sprinkle the top of the casserole with the extra cheese, then bacon, then thyme.
Bake uncovered for one hour. In the last 15 minutes of baking, turn the oven up to 375F to get a nice crusty brown around the edges.