Preheat oven to 400 degrees F. Coat a deep baking dish (I used a 13" x 8" dish) with the butter.
Combine the cheeses into a large mixing bowl. Remove 1/3 of the cheese to a separate bowl and set aside. Add in the half and half, salt, pepper, garlic powder, onion powder, and thyme to the remaining cheese mixture.
Add the potato slices and toss to thoroughly coat, making sure to get every potato slice.
Grab a handful of potato slices and add them to the prepared baking dish in a stack. Start by lining them up along the edge, creating a circle around the dish. Continue lining up the potato slices until the entire casserole dish is full and tightly packed. Depending on your dish, you may need to peel and slice an additional potato or two to fill the dish.
Pour whatever cream and cheese mixture is left in the mixing bowl over the top of the potato slices. Don't fill the dish all the way full. You want the liquid to fill half the dish. Discard any leftover liquid.
Cover the baking dish with aluminum foil and bake for 30 minutes. Remove the dish from the oven to remove the foil and return it to bake for an additional 30 minutes.
Add the remaining shredded cheese to the top and return to bake 20-30 more minutes. Or until the top of the potatoes has reached a crispy, golden brown.
Allow the potatoes to rest for 5 minutes before slicing into. Garnish with additional thyme, chives, or grated parmesan cheese.