Preheat oven to 425F.
Line a ½ sized heavy aluminum, high-sided sheet pan with parchment paper. Butter the paper liberally (1/4 cup). Peel and slice the potatoes using a mandolin set on the next to the thinnest setting (i.e. very thin). Mix the cream, cheeses, nutmeg, and the salt and pepper in a bowl. Layer the potato slices on the buttered paper. Drizzle mixture on each layer. Repeat to make about 6 layers. Finish the top layer with remaining mixture and dollop with remaining butter. Tent with aluminum foil and bake until potatoes are very soft (about 1 hour), remove foil at the end of cooking to achieve a brown top. Let stand for 15-20 minutes. Slide or cut as desired.
Slide lamb loin on a bias and arrange all elements as desired to serve.
Keep up to date on the latest wine releases, events, and promotions.