Begin by preheating your oven to 275°F (140°C) and lightly buttering a shallow gratin dish. While the oven heats, prepare your cream mixture by combining ⅔ cup of half-and-half and ⅔ cup of heavy cream in a bowl with 1 large crushed garlic clove, stirring well to distribute the garlic evenly throughout the liquid.
This slow infusion of garlic flavor will permeate every layer of the finished dish without overpowering it. Peel and thinly slice 2 lb (1 kg) of Yukon gold potatoes, preferably using the slicing disc of a food processor for uniform thickness—consistent potato slices guarantee even cooking throughout the gratin.
Layer the sliced potatoes in the buttered gratin dish, seasoning each layer generously with salt and black pepper. Pour the garlic-infused cream mixture over the potatoes, making sure it seeps between the layers to create that signature creamy interior.
The potatoes will absorb much of the liquid during baking, so don't be concerned if the cream level seems high initially. Top the entire gratin with 4 oz (125 g) of grated Gruyère cheese, distributing it evenly across the surface to ascertain a golden, cheese-studded crust develops during baking.
Bake the gratin for 1½ hours at 275°F until the potatoes are completely tender when pierced with a knife and the cheese topping has turned a rich golden brown. The low, gentle heat allows the potatoes to cook through slowly without the edges becoming dry or overcooked.
Serve the gratin immediately while it's still piping hot and the cheese is at its most creamy and luxurious—this dish is best enjoyed fresh from the oven.
