Gratin de chou-fleur is the classical cauliflower gratin — blanched cauliflower florets napped with sauce Mornay (béchamel enriched with Gruyère and egg yolks) and gratinéed until the sauce bubbles fiercely and develops a deep golden-brown crust spotted with dark, almost charred patches. This preparation is the template for an entire family of vegetable gratins in the French repertoire — the same Mornay-and-gratinée approach applies to broccoli, leeks, endives, and cardoons with equal success. The technique requires careful blanching: separate a large cauliflower into even-sized florets (uniformity ensures even cooking) and blanch in heavily salted, rapidly boiling water with a squeeze of lemon juice (which maintains whiteness) for 5-7 minutes until just tender — a knife point should meet slight resistance, as the cauliflower will cook further under the sauce. Drain thoroughly and arrange in a single layer in a buttered gratin dish. Prepare the Mornay sauce: make a medium béchamel (40g butter, 40g flour, 500ml milk), season with salt, white pepper, and nutmeg, then off the heat whisk in 2 egg yolks and 100g of finely grated Gruyère (or a mixture of Gruyère and Parmesan). The sauce should be thick enough to coat the cauliflower without sliding off — thicker than a standard béchamel but still pourable. Nappé the cauliflower generously, ensuring every floret is well coated. Scatter an additional 50g of grated Gruyère over the surface and dot with small pieces of butter. Gratinée at 220°C for 15-18 minutes, or under a hot grill for 8-10 minutes, until the sauce bubbles violently, the surface is deep golden-brown with dark spots, and the edges are crisp and caramelised. The interior should be a harmony of tender, faintly sweet cauliflower and rich, cheesy, savoury sauce — each element elevating the other. Serve immediately in the gratin dish.
Cauliflower blanched until just tender (5-7 min) — will cook further under sauce. Lemon in blanching water maintains white colour. Mornay sauce: béchamel + egg yolks + Gruyère — thick enough to coat without sliding. Additional cheese and butter on top for the gratin crust. 220°C until bubbling fiercely and deep golden-brown.
A tablespoon of Dijon mustard whisked into the Mornay adds hidden sharpness that elevates the whole dish. For a lighter gratin, use velouté instead of béchamel as the sauce base. Toast breadcrumbs mixed with the cheese topping add textural contrast. The same preparation with broccoli (gratin de brocoli), leeks (poireaux gratinés), or Belgian endive (endives au gratin, wrapping each in ham first) are all equally classical. Individual gratin dishes provide a better crust-to-filling ratio than one large dish.
Over-blanching the cauliflower, producing mush under the sauce. Mornay too thin — it must coat and cling, not pool at the bottom. Not draining cauliflower thoroughly, diluting the sauce with water. Under-gratinéeing — the surface needs aggressive colour and bubbling. Using only mild cheese, producing an insipid gratin — Gruyère's sharpness is essential.
Le Guide Culinaire — Auguste Escoffier