Scalloped Potatoes au Gratin

Ingredients

Equipment Needed

• •9x13 inch baking dish or 3-quart gratin dish
• •Mandoline or sharp chef's knife
• •Medium saucepan
• •Fine-mesh strainer
• •Rimmed baking sheet
• •Aluminum foil

Instructions

1. 1

   Infuse the cream

   Combine the heavy cream, milk, smashed garlic, thyme sprigs, bay leaf, salt, white pepper, and nutmeg in a medium saucepan. Set over medium heat and bring just to a simmer. Watch carefully. You want small bubbles forming around the edges, not a rolling boil. Once it simmers, remove from heat, cover, and let steep for 20 minutes. The cream will turn slightly golden and smell intensely of garlic and thyme. This is where your gratin's soul develops.

   White pepper disappears into the cream without leaving black specks. If you only have black pepper, use it freely. Taste trumps appearance.
2. 2

   Prepare the baking dish

   Use 2 tablespoons of the softened butter to generously coat a 9x13 inch baking dish or a 3-quart gratin dish. Get into the corners. Butter prevents sticking and contributes to the crust formation on the edges, where the cream caramelizes against the hot ceramic.

3. 3

   Slice the potatoes

   Using a mandoline or sharp knife, slice the potatoes into rounds about 1/8 inch thick. Uniformity matters here. Uneven slices cook at different rates, leaving you with some pieces mushy and others still crunchy. Keep the sliced potatoes in a bowl of cold water to prevent browning if you're working slowly, but drain and pat them completely dry before layering.

   A mandoline set to 3mm produces ideal slices. Use the hand guard. I've seen too many cooks sacrifice fingertips to impatience.
4. 4

   Strain the cream

   Pour the infused cream through a fine-mesh strainer into a large measuring cup or bowl. Press on the garlic cloves with a spoon to extract every drop of flavor. Discard the solids. Taste the cream. It should be well-seasoned. Add more salt if needed. The potatoes will absorb much of the seasoning, so the cream should taste slightly saltier than you'd want to drink.

5. 5

   Build the first layer

   Preheat your oven to 350°F. Arrange a single layer of potato slices in the prepared dish, overlapping them like roof shingles. Each slice should cover about a third of the previous one. Season lightly with salt. Scatter about 3/4 cup of Gruyère over the potatoes. Ladle enough cream to barely cover the layer, roughly 1/2 cup. The cream should pool around the edges but not submerge the potatoes completely.

6. 6

   Continue layering

   Repeat the layering process: overlapping potato slices, light seasoning, Gruyère, cream. You'll build about 5 to 6 layers depending on your dish's depth. Press down gently on each layer before adding the next. This eliminates air pockets and ensures the cream penetrates throughout. Reserve about 1/2 cup of Gruyère and all of the Parmesan for the top.

7. 7

   Finish the top

   For the final layer, arrange your prettiest potato slices in a decorative pattern. Pour any remaining cream over the top. Combine the reserved Gruyère with the Parmesan and scatter evenly across the surface. Cut the remaining 2 tablespoons of butter into small pieces and dot them across the cheese. This extra fat promotes browning and adds richness to the crust.

8. 8

   Begin the bake covered

   Cover the dish tightly with aluminum foil, tenting it slightly so the foil doesn't touch the cheese. Place on a rimmed baking sheet to catch any bubbling overflow. Bake for 1 hour. The covered phase allows the potatoes to steam and cook through without the top browning too quickly.

9. 9

   Uncover and brown

   Remove the foil and continue baking for 25 to 35 minutes. Watch the color develop. You're looking for deep golden brown patches across the surface, with cream bubbling vigorously around the edges. The center should jiggle slightly when you shake the dish, like a custard that's just set. A knife inserted in the center should meet no resistance from the potatoes.

   If the top browns before the potatoes are tender, tent loosely with foil and continue baking. Better a pale top than crunchy potatoes.
10. 10

    Rest before serving

    Remove from the oven and let rest for 15 to 20 minutes. This resting period is not optional. The gratin needs time to set. Cut into it immediately and you'll have cream running everywhere and layers collapsing. Wait, and the starches firm up enough to hold their shape when you scoop out a portion. The dish stays hot for a remarkably long time. Garnish with snipped chives and serve directly from the baking dish at the table.

Chef Tips

• •Yukon Golds strike the ideal balance between waxy and starchy. They hold their shape while releasing enough starch to thicken the cream. Russets work but can turn mealy. Red potatoes stay too firm. Stick with Yukons.
• •Grate your own cheese from a block. Pre-shredded cheese contains anti-caking agents that prevent smooth melting. The difference is noticeable. You'll taste it in the sauce and see it in how the top browns.
• •For a lighter version, replace half the cream with whole milk. The result is less rich but still satisfying. Don't attempt this with skim milk or the sauce will break.
• •A crisp white Burgundy or California Chardonnay complements the richness beautifully. The wine's acidity cuts through the cream while echoing the nuttiness of the Gruyère.
• •Leftovers reheat beautifully. Cover with foil and warm at 325°F until heated through, about 20 minutes. The texture actually improves as the starches continue to bind.

Advance Preparation

• •The complete gratin can be assembled up to 24 hours ahead, covered tightly, and refrigerated. Add 15 to 20 minutes to the covered baking time since you're starting from cold.
• •Infused cream can be prepared up to 2 days ahead and refrigerated. Reheat gently before using.
• •For day-of convenience, peel and slice potatoes in the morning. Store submerged in cold water in the refrigerator. Drain and dry thoroughly before layering.
• •The fully baked gratin can be made one day ahead, cooled, covered, and refrigerated. Reheat at 325°F, covered, for 30 to 40 minutes until bubbling. Uncover for the final 10 minutes to re-crisp the top.

Frequently Asked Questions

Nutrition Information

1 serving (about 385g)