Preheat oven to 400 degrees.
Peel, and very thinly slice both types of potatoes.
In a large skillet, pour and begin to heat heavy cream, half of the thyme leaves, and nutmeg.
Place potatoes in cream mixture and boil for 3-4 minutes.
Remove potatoes from heat and let them cool slightly.
In a baking dish, line the pan with 1/3 of the potatoes and top with 1/3 of manchego and gruyere cheese.
Repeat with a second layer, and then top with remaining 1/3 of potatoes.
Pour heavy cream from pan over the potatoes and top the dish with the remaining 1/3 of cheese.
Bake in 400 degree oven for 35 minutes, broil for two additional minutes to brown the top.
Let cool for 10-15 minutes and top with remaining fresh thyme before serving.