Leek Gratin

Ingredients

Equipment Needed

• •Wide skillet with lid (12-inch)
• •Shallow oval gratin dish (2-quart)
• •Microplane or fine grater for nutmeg

Instructions

1. 1

   Trim and clean the leeks

   Cut away the dark green tops where the color shifts from pale to deep. Trim the root ends but leave enough to hold the layers together. Slice each leek in half lengthwise and hold them under cold running water, fanning the layers to flush out any grit hiding between them. Leeks grow in sandy soil and trap dirt in their folds. Take your time here.

   Save those dark green tops for stock. They have flavor to give, just not the tender sweetness you want for this dish.
2. 2

   Braise the leeks

   Melt the butter in your widest skillet over medium heat. Arrange the leek halves cut-side down in a single layer, working in batches if needed. Let them cook undisturbed for 4 to 5 minutes until the cut surfaces turn golden. Flip them, add a generous pinch of salt, and pour in the stock. Cover and reduce the heat to medium-low. Braise for 15 to 20 minutes, until a knife slides through without resistance. The leeks should be completely tender but still hold their shape.

3. 3

   Prepare the gratin dish

   Preheat your oven to 400F. Rub a shallow baking dish with a bit of soft butter. The dish should hold the leeks snugly in a single layer. Oval gratin dishes work beautifully here, about 2 quarts.

4. 4

   Layer the gratin

   Transfer the braised leeks to the prepared dish, arranging them cut-side up. Pour any buttery braising liquid from the pan over them. Scatter half the thyme leaves across the leeks. Pour the cream evenly over everything, letting it pool around and between the pieces. The cream should come about halfway up the sides of the leeks, not cover them completely.

5. 5

   Add cheese and seasonings

   Grate the nutmeg directly over the cream. Grind black pepper generously across the surface. Scatter the gruyère in an even layer, concentrating it over the leeks themselves rather than the edges of the dish where it might burn. Reserve a tablespoon of thyme for finishing.

6. 6

   Bake until golden

   Bake uncovered for 25 to 30 minutes. The gratin is ready when the cream bubbles vigorously around the edges, the cheese forms a deeply golden crust with spots of brown, and the center no longer looks liquid. The aroma should fill your kitchen with sweet allium and nutty cheese. Let it rest for 5 minutes before serving. Scatter the remaining thyme leaves over the top.

   If the cheese browns before the cream reduces and bubbles properly, tent loosely with foil and continue baking.

Chef Tips

• •At the farmers' market, choose leeks that feel heavy for their size with no soft spots. The darker green tops should still look vital. Ask when they were harvested. Same day or yesterday is ideal.
• •Age matters with gruyère. Look for wheels aged at least 10 months. Young gruyère melts into blandness. Properly aged cheese has nuttiness and complexity that stands up to the sweet leeks.
• •This dish wants a dry white wine alongside it. Something from the Loire, perhaps, or a Chablis. The acidity cuts through the cream beautifully.
• •If leeks are out of season, do not force it. Wait for them, or make a similar gratin with fennel or Belgian endive, which share that willingness to become silky under heat.

Advance Preparation

• •Leeks can be braised a day ahead and refrigerated. Bring to room temperature before assembling the gratin.
• •The assembled but unbaked gratin can wait, covered, in the refrigerator for up to 6 hours. Add 5 to 10 minutes to the baking time if starting cold.
• •Leftovers reheat gently in a 325F oven, covered with foil, for 15 minutes. The cheese will not crisp again, but the flavor deepens.

Frequently Asked Questions

Nutrition Information

1 serving (about 200g)