Preheat oven to 375 degrees
Wash and peel potatoes. Slice them very thinly using a mandolin slicer. Add the sliced potatoes to a large bowl
Cut the onion in half, peel and slice thinly into the bowl of potatoes
Pour heavy cream over the potatoes, plus the seasonings and cheese (reserve about ½ cup for sprinkling over the top)
Toss the potatoes in the cream mixture until well coated, then layer the potatoes in a large, buttered baking dish
Pour any remaining heavy cream mixture in bowl over the stacked potatoes. Cover and bake for roughly 35-40 minutes, until bubbly
Uncover, sprinkle remaining cheese over top and bake for 30 minutes, or until cheese is slightly browned
Garnish with fresh thyme (optional)
