Spinach Gratin

Three pounds of fresh spinach cooks down to a fraction of its volume, gets squeezed bone dry, chopped, and mixed with butter and nutmeg. That concentrated spinach base goes into a gratin dish, gets blanketed with Mornay sauce (a béchamel enriched with cheese), and topped with Gruyère before baking until golden and bubbling at the edges.

Squeezing every drop of water out of the cooked spinach is what separates a great gratin from a watery one. The recipe is specific about this: use the back of a spoon in a strainer first, then squeeze handfuls with your hands. Wet spinach dilutes the Mornay sauce and you end up with a soupy dish instead of a rich, creamy gratin.

Nutmeg is the classic French pairing with spinach, and for good reason. Just a grating adds a warm, slightly sweet note that makes the spinach taste more like itself. Too much tastes medicinal, so go easy.

Chef Tips

• Use a non-aluminum pot for cooking the spinach. Aluminum reacts with spinach’s oxalic acid and can give it a metallic taste and discolor the leaves.
• Squeeze the spinach ruthlessly. You cannot overdo this. Every bit of water left in the spinach weakens your gratin. The spinach should feel almost dry to the touch before chopping.
• Make the Mornay sauce slightly thicker than usual. Since the spinach releases a small amount of liquid during baking, a thicker sauce holds up better and stays creamy instead of running thin.
• Bake until bubbly at the edges but not dried out. Twenty minutes at 375°F (190°C) should do it. The Gruyère should be golden and the sauce should be visibly bubbling at the edges of the dish.

Variations

• Creamed spinach shortcut: Skip the Mornay and mix the spinach with ½ cup heavy cream and the Gruyère for a simpler, still-rich version.
• Add garlic: Sauté 2 minced garlic cloves in the butter before mixing with the spinach for a more assertive flavor.