Preheat oven to 350 degrees.

In a small saucepan, melt butter. Add shallots and cook, stirring continuously, until tender. Add thyme and cook for another minute. Remove from heat and set aside.

Peel potatoes and thinly slice into rounds using a mandolin.

Grease a 9x13 baking dish.

Layer 1/3 of the potatoes into the dish. Season with 1/3 of the salt and pepper. Add 1/3 of the shallots, spread out evenly. Sprinkle 1/3 of the guyrere and cheddar.

Repeat this process 3 times.

In a small saucepan, heat the heavy cream over medium heat until simmering. (Add in a few sprigs of thyme for extra flavor. Remove when cream is heated).

Pour cream over potatoes.

Cover with aluminum foil and bake for 1 hour.

Remove foil and bake an additional 30 minutes.

Let set for at least 15 minutes before serving. Add more thyme for garnish.