Root Vegetable Gratin

Ingredients

Equipment Needed

• •Shallow baking dish, roughly 25cm, the kind that goes from oven to table
• •Mandoline or sharp knife
• •Small saucepan for the cream

Instructions

1. 1

   Warm the cream

   Set the oven to 180C/160C fan. Butter a baking dish generously, the kind that goes straight to the table. Pour the cream into a small saucepan and add the crushed garlic, thyme leaves, a good grating of nutmeg, and a generous pinch of salt. Warm it gently until it just begins to tremble at the edges. Don't let it boil. You want the flavours to open up and the kitchen to start smelling like the sort of evening where you're not going anywhere. Take it off the heat and let it sit while you deal with the vegetables.

   The cream infusion is doing the real work here. Give it ten minutes off the heat with the garlic and thyme, and it will carry more flavour into the dish than any amount of seasoning between the layers.
2. 2

   Slice the roots

   Peel the celeriac, parsnips, and potatoes. Slice them all thinly, about the thickness of a coin. A mandoline makes short work of this if you have one, but a sharp knife and some patience will do. The celeriac will oxidise and go brown if you leave it sitting around, so drop the slices into a bowl of cold water as you go. Drain and pat dry before you start layering.

   Evenness matters more than precision. You want the slices roughly the same thickness so they cook through at the same rate. If some are a bit thicker, put those on the bottom of the dish where they'll get more time in the heat.
3. 3

   Build the layers

   Start with a layer of potato on the bottom of the buttered dish, overlapping the slices slightly like fallen tiles. Season with salt and pepper. Follow with a layer of celeriac, then parsnip, seasoning as you go. Pour a little of the infused cream over each layer, enough to pool between the slices. Repeat until you've used everything, finishing with a layer of potato on top. Pour over the remaining cream. It should come about three-quarters of the way up the dish. Press the top layer down firmly with your palm so everything settles.

4. 4

   Bake covered

   Dot the surface with small pieces of butter and cover the dish tightly with foil. Bake for forty-five minutes. The cream should be bubbling gently at the edges and a knife should slide into the centre without any resistance. If the roots still feel firm, give it another ten minutes. They need to be completely soft. This isn't a dish that forgives undercooking.

5. 5

   Finish with cheese

   Remove the foil. Scatter the grated cheese over the top in an even layer. Return to the oven, uncovered, for another twenty to twenty-five minutes, until the top has gone deep gold and the cream is thick and bubbling up through the cheese at the edges. The smell at this point will tell you everything you need to know. Let it rest for ten minutes before you bring it to the table. It needs that time to settle, and you need it to stop being too hot to eat. Serve it straight from the dish.

Chef Tips

• •The thickness of your slices determines whether this works. Too thick and the roots won't cook through in time; too thin and they'll dissolve into the cream and lose all texture. Aim for the thickness of a one-pound coin. You don't need a ruler. You need a sharp knife and a steady hand.
• •Celeriac is the quiet hero here. It has a sweetness and a celery-like depth that the other roots don't, and it softens into something almost silky in the cream. Don't skip it. If you can't find one, use more parsnip, but the dish will be sweeter and simpler for it.
• •A gratin reheats beautifully. Leftover slices, warmed in a moderate oven until the cream starts to bubble again, are one of the better things you can eat for lunch the next day. A green salad on the side, dressed sharply with mustard and lemon, and you're sorted.
• •If you want to make this a full meal, it stands alone with a good salad. If it's alongside something, roast chicken or a slow shoulder of lamb, keep the portions modest. It's rich. A square the size of your palm is enough.

Advance Preparation

• •The gratin can be assembled, covered, and refrigerated up to a day ahead. Add fifteen minutes to the covered baking time if it goes into the oven cold.
• •Keeps well in the fridge for up to three days. Reheat individual portions in a moderate oven until the cream bubbles at the edges. The microwave will do in a pinch, but the oven gives you back the crust.

Frequently Asked Questions

Nutrition Information

1 serving (about 400g)