- 1.2 kg (about 2.5 pounds) starchy potatoes such as Russet, Yukon Gold, or Desiree, peeled and thinly sliced approximately 3 millimeters (one-eighth inch) thick
- 1 and a half cups heavy cream (thickened cream)
- 3 cloves garlic, minced or very finely grated
- 1 small yellow onion, very thinly sliced (optional but adds wonderful sweetness and depth)
- 2 tablespoons unsalted butter, cut into small pieces
- 1 teaspoon fine salt, plus more to taste
- Half a teaspoon freshly ground black pepper
- A pinch of freshly grated nutmeg (optional but traditional and highly recommended)
- 1 and a half cups grated cheese — a good melting cheese like cheddar, Gruyère, Comté, or a combination of cheddar and mozzarella
- Fresh thyme leaves or finely chopped fresh parsley for garnish (optional)
Instructions
Step 1: Prepare the Potatoes and Oven
Preheat your oven to 180 degrees Celsius (350 degrees Fahrenheit). Peel the potatoes and slice them as thinly and evenly as possible — a mandoline slicer produces the most consistent results and makes the process considerably faster, but careful knife work produces equally good results if you take care to keep the slices uniform. Uniformity is genuinely important here: slices of different thicknesses will cook at different rates, and you can end up with some slices perfectly tender while others are still firm in the center. Aim for approximately 3 millimeters, which is about one-eighth of an inch. You do not need to rinse the sliced potatoes — the surface starch that remains on them after slicing is exactly what will help thicken the cream sauce as it bakes.
Step 2: Make the Cream Mixture
In a small bowl or measuring cup, combine the heavy cream with the minced garlic, salt, pepper, and nutmeg if using. Stir well to fully combine. This seasoned cream mixture is what will be poured over the potato layers and will become the sauce as the dish bakes. Taste the cream and adjust the seasoning — the cream should taste pleasantly seasoned at this stage, as the potatoes will absorb and dilute the saltiness somewhat during baking.
