Author Alice Hart says: “A more indulgent recipe than I habitually write; I don’t typically use a lot of rich cream or dairy-based sauces, preferring the clout of chilli, citrus, flavourful oils and dressings, fresh herbs, toasted nuts and the like to the sometimes cloying richness of a cheese sauce. But this is a nod to Christmas and with Christmas come the rich exceptions.”

Serves 6 (as a side)

Preparation time: 30 minutes

Cooking time: 1 hour 30 minutes

Ingredients

500g (1lb 2oz) slender parsnips
1½ tbsp olive oil
200g (7oz) dried rigatoni, penne or similar short pasta tubes
200g (7oz) raw Brussels sprouts, trimmed and sliced
450ml (153/4fl oz) whole milk
2 fat garlic cloves, bruised
3 bay leaves, bruised
7 thyme sprigs
1½ tsp freshly grated nutmeg
30g (1oz) butter
30g (1oz) spelt flour or plain (all-purpose) flour
200ml (7fl oz) crème fraîche
250g (9oz) Gruyère coarsely grated
3 tbsp finely grated, vegetarian parmesan-style cheese
90g (3oz) walnuts, roughly crushed
Salt and freshly ground black pepper

Method

Preheat the oven to 180°C (350°F/gas 4).

Top, tail and peel the parsnips and reserve the peelings and trimmings. Cut the parsnips into thumb-sized pieces or slices and toss with the oil. Spread out in a roasting pan in a single layer, season with salt and pepper and roast for 35–40 minutes, shimmying halfway through until just tender and turning golden.

Meanwhile, cook the pasta in a large saucepan of plenty of boiling salted water for 3 minutes, then add the sliced Brussels sprouts and simmer for a further 2 minutes. Drain in a colander, refreshing very briefly under cool water. Put the milk in the same (empty) pasta pan with the bruised garlic and bay, 4 of the thyme sprigs and 1 teaspoon of the nutmeg. Add the parsnip peelings and simmer gently for 10 minutes, then remove from the heat, cover and leave to sit for 15 minutes. Strain the flavoured milk into a jug.

Rinse out the pan and return it to a lowish heat with the butter and flour, stirring with a wooden spoon to make a paste. Cook this out for 4–5 minutes, really toasting the flour and letting it fizz. Now scrape the roux to one side of the pan and slosh about 150ml (5fl oz) of the infused milk into the empty part of the pan, allowing it to heat through slightly before briskly whipping it into the roux with a balloon whisk. Letting the milk heat through first will help prevent lumps forming. Keep going in this way, adding the milk, but giving it a moment to warm through before whisking in, until it has all been incorporated. Now whisk in the crème fraîche and bring the mixture to a gentle boil. Simmer this rich sauce, stirring, for 5 minutes to cook out every remnant of flour taste, then remove from the heat and add the cheeses with the remaining 1/2 teaspoon of grated nutmeg. Leave for 2 minutes, then stir well and season to taste.

Add the pasta, sprouts and roast parsnips to the sauce, folding everything together. The melted Gruyère cheese will have made its elasticated presence known by this point. Spoon into a 20 x 30cm (8 x 12in) baking dish and top with the leaves from the remaining 3 thyme sprigs and the crushed walnuts.

Bake the gratin in the oven for about 25 minutes until the nuts are golden and the edges bubbling.

From The Magnificent Book of Vegetables by Alice Hart (£24.70, Welbeck).

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