Prepare the potatoes

• Peel the potatoes and slice them into thin, even rounds.
• Keep the slices in cold water so they do not brown.

Infuse the cream mixture

• Pour the milk and heavy cream into a saucepan.
• Add the crushed garlic, bay leaf, thyme sprigs, grated nutmeg, salt and pepper.
• Warm gently over low heat without boiling to infuse the aromas.

Layer the gratin

• Butter the baking dish generously.
• Arrange the potato slices in overlapping layers.
• Pour the warm cream mixture over the potatoes, straining out the aromatics.

Add the cheese

• Scatter the grated Gruyère and Parmesan evenly over the surface.

Bake the gratin

• Bake until the potatoes are tender and the top is golden and bubbling.
• Let it rest a few minutes before serving.