Step 1

Preheat oven to 375°F (190°C). Melt butter in a saucepan set over medium. Add onion, thyme and garlic. Cook for 5 minutes or until softened. Stir in soup, broth, black pepper, nutmeg and salt. Bring to a simmer.

Step 2

Meanwhile, layer one-third of the potatoes, overlapping slightly, in a greased 9x13-inch (3 L) baking dish. Sprinkle with 1/3 cup (75 mL) Gruyere cheese and top with one-third of the broth mixture. Repeat the layers twice.

Step 3

Press down on the potatoes to make sure they are immersed in liquid. Sprinkle the remaining Gruyere cheese and Parmesan cheese on top. Cover the surface directly with parchment paper then cover the pan with aluminum foil and place on baking sheet.

Step 4

Bake for 60 minutes; remove aluminum foil and parchment paper. Bake for an additional 60 minutes or until potatoes are tender and cheese has browned. Let stand for 10 minutes before serving.