Company-Worthy Creamy Potato Gratin (Golden & Bubbly)

Prep and preheat: Heat oven to 375°F (190°C). Butter a 9×13-inch (23×33 cm) baking dish.
Heat the cream: In a saucepan, combine cream, milk, butter, garlic, 1 teaspoon salt, pepper, and nutmeg. Heat until steaming and butter melts; do not boil.
Layer: Arrange one third of potatoes in the dish, overlapping slightly. Sprinkle with one third of Gruyère and a tablespoon of Parmesan plus a pinch of the remaining 1/2 teaspoon salt. Repeat two more times.
Pour and press: Pour hot cream mixture evenly over layers. Press gently to submerge all slices and remove air pockets.
Bake covered: Cover tightly with foil and bake 40 minutes until potatoes are nearly tender.
Brown the top: Remove foil, add remaining cheeses, and bake 20–30 minutes more until deep golden and bubbling at the edges.
Rest and serve: Let stand 10–15 minutes to set. Finish with herbs and slice into squares.

Troubleshooting & Consistency Tips

Watery gratin: Ensure the cream mixture is hot when poured; cold liquid prolongs cooking and can weep. Bake until the edges bubble vigorously.
Top browning too fast: Tent loosely with foil during the last 10 minutes or move to a lower rack.
Potatoes still firm: Slice thinner (3 mm) and keep covered longer before the final browning stage.
Greasy pool on top: Avoid boiling the cream and measure cheese accurately; too much fat can separate.
No mandoline: A sharp knife works; keep slices as uniform as possible for even cooking.

Storage & Make-Ahead

Refrigerate: Cover leftovers and chill up to 4 days. Reheat, covered, at 325°F (165°C) until hot, then uncover for 5 minutes to re-crisp the top.

Freeze: Cool completely, wrap well, and freeze up to 2 months. Thaw overnight in the refrigerator and reheat as above.

Make ahead: Assemble through step 4 up to 24 hours in advance. Cover and refrigerate. Add 10–15 minutes to the covered bake time if starting cold.

Why This Recipe Works

Heating the cream with butter and aromatics dissolves fat uniformly and jump-starts starch gelatinization, which sets the sauce into a velvety nap rather than a thin soup.
Layering cheese between the potatoes seasons every bite and stabilizes the sauce, while a final uncovered bake evaporates excess moisture and forms a savory browned crust.
Resting is crucial; it allows the starches to firm up, so slices stand tall on the plate.

Expert Tips

Flavor boosters: Rub the dish with a cut garlic clove before buttering, or add a teaspoon of Dijon to the cream for gentle tang.
Cheese swap: Comté, Emmental, or sharp cheddar all work; keep Parmesan for the top for best browning.
Scaling: For two trays, double all ingredients and bake on separate racks, rotating pans halfway.