Preheat oven to 375 F.
Peel and slice the potatoes (⅛-inch thickness). Using a mandolin slicer can be quite handy and a nice time saver for this process. Peeling and slicing should take about 15-20 minutes depending on your skill level (and potential helpers you have in the kitchen).
Next, you will want to add all the ingredients besides the pototoes and butter to a medium-sized bowl and mix together thoroughly with a fork or whisk.
With the softened butter, coat the bottom and sides of a 8 x 8 casserole dish.
You will prepare the dish for the oven by layering half of the potatoes in an overlapping fashion in the buttered casserole dish, trying not to lie any of them flat on the bottom. This is not a science, however, and it’s really hard to mess it up. You just want the potatoes to slightly overlap and be somewhat even overall.
After layering half of the sliced potatoes, you will then cover them with half of the sauce mixture. Then you will layer the other half of the sliced potatoes and top with the remaining sauce.
Before putting in the oven, you will cover with foil and place on a cookie sheet to catch any spillage.
Bake for one hour covered.
After one hour, uncover and check doneness level with a fork or knife. Cook uncovered 30-45 more minutes or until potatoes are done and top is browned.