Wash and thin slice the leek
Sauté the sliced leek and minced garlic in butter until the leek is fully cooked
Cool the cooked leaks if assembling ahead of time
Slice potatoes thinly using a knife or mandolin
Layer potatoes vertically in a baking dish, alternating with the cooked leaks and other ingredients
Pour heavy cream over the layers (about ¼ cup per potato)
Season with salt, pepper, thyme leaves, and onion powder
Top with Parmesan and Emmental cheese
Cover tightly with foil and bake at 375°F for about 1 hour and 15 minutes until potatoes are fully cooked
Remove foil, increase oven temperature to 425°F, add more Parmesan cheese on top
Bake for 10-15 more minutes until bubbling and golden
Let cool slightly before serving
