Slow-cooking in fat, or confiting, to use the fancy term, is usually associated with meat (or for preserving fruit in sugar syrup). For me, however, vegetables are the biggest winners from a long, warm bath of oil and aromatics. In the process (which isn’t actually that long with veg), they tenderise and soak up a bunch of flavours that make them rich, unctuous and delicious. It’s a total transformation of something mild and humble into something rich and luxurious. All they then need is a spot of acidity or a touch of heat, and you’ve got glorious vegetables, reimagined, on the table.

Portobello mushrooms with chilli oil and butter bean puree (pictured above)

This is a sort of vegan equivalent of steak and mash. The oil the mushrooms are cooked in turns into something similar to harissa, with a deep, umami flavour and a real kick, so leave out the red chilli if you prefer less heat. This will make more oil than you need: keep any excess in a sealed container in the fridge, for spooning over grilled veg or meat.The mash can be warmed up or served at room temperature.

Prep 15 min

Cook 1 hr 35 min

Serves 4 as a main

For the mushrooms

8 medium to large portobello mushrooms (about 650g), stems removed

10 garlic cloves, peeled

1 onion, peeled and cut into 6 wedges

1½ tbsp chipotle chilli flakes

1 red chilli

4 tsp cumin seeds, roughly crushed in a mortar

1 tbsp coriander seeds, roughly crushed in a mortar

2 tbsp tomato paste

400ml olive oil

1 tbsp flaked sea salt

For the puree

500g freshly cooked or good-quality jarred butter beans (drained weight)

1½ tbsp lemon juice

1 tbsp olive oil

½ tsp flaked salt

Heat the oven to 170C (150C fan)/335F/gas 3. Put the mushrooms domed side up in a large, ovenproof saucepan for which you have a lid, and arrange the garlic and onion in and around them. Add all the remaining mushroom ingredients, then cover with a piece of greaseproof paper, push it down gently to cover the mix, then top the pan with a lid. Bake for an hour, then remove the pan, turn over the mushrooms, replace the paper and lid, and bake for 20 minutes more, or until the mushrooms are very tender but not falling apart. Use a pair of tongs to transfer the mushrooms to a board, cut them in half and set aside.

Use a spoon to lift the onion, garlic and chilli (discard the stem) out of the oil – don’t worry if you scoop up some of the spices and oil, too – put in the small bowl of a food processor and blitz smooth. Return the onion mixture and mushroom halves to the saucepan, put on a medium-high heat and cook for five minutes, so all the flavours come together.

Meanwhile, make the puree by blitzing all the bean ingredients in a food processor with two tablespoons of water, until completely smooth. If you prefer a warm mash, transfer to a saucepan and heat gently.

Divide the puree between four plates, top each portion with four mushroom halves and generously spoon over the oil and its solids.

Brussels sprouts, chestnuts and grapes

This dish is made special by the complex sweetness and depth of Shaoxing wine, a Chinese wine fermented from rice that you can now find in large supermarkets and most Asian food stores – if you can’t get it, use pale dry sherry instead. Get ahead by cooking the shallots, garlic, chestnuts and grapes a day ahead, and leave them to sit in the liquid in the fridge overnight, but don’t roast the sprouts until the day.

Yotam Ottolenghi’s brussels sprouts, chestnuts and grapes. Photograph: Louise Hagger/The Guardian. Food styling: Emily Kydd. Prop styling: Louie Waller.

Prep 20 min

Cook 70 min

Marinate 30 min- 1 hr

Serves 4 as a side

12 small shallots, peeled and left whole

5 cloves garlic, peeled and crushed with the flat of a knife

250g ready-cooked and peeled chestnuts

4 fresh bay leaves

1 tbsp maple syrup

130ml olive oil

80ml Shaoxing rice wine (or pale dry sherry)

60ml soy sauce

180g seedless red grapes

800g brussels sprouts, trimmed and halved lengthways

Salt

2 green chillies, cut into thin rounds

2 tbsp rice vinegar

1 tsp caster sugar

3 tbsp parsley leaves

Heat the oven to 180C (160C fan)/350F/gas 4. Put the first five ingredients in a large 34cm x 26cm, high-sided roasting tin, then add 100ml oil, 75ml rice wine and two tablespoons of soy sauce. Cover tightly with foil and roast for 35 minutes, until the shallots are soft but still hold their shape. Stir in the grapes, cover again with foil, cook for 10 minutes more, then remove from the oven, discard the foil and set aside the tin while you roast the sprouts.

Turn up the oven to 240C (220C fan)/465F/gas 9. Toss the sprouts in two tablespoons of oil and a quarter-teaspoon of salt, then spread them out on two oven trays lined with baking paper. Roast for 16 minutes, switching the position of the trays halfway through, until browned, then tip the sprouts into the shallot tin, gently mix everything together and leave, uncovered, at room temperature for an hour, ideally, and at least 30 minutes, to give the flavours time to develop.

Meanwhile, in a small bowl mix the chillies, rice vinegar, sugar and an eighth of a teaspoon of salt, and leave to pickle for at least 30 minutes.

Once the sprouts have sat for a while, stir in the remaining teaspoon of rice wine and two tablespoons of soy sauce, and the parsley, and transfer to a large, shallow bowl. Top with the pickled chillies and their pickling liquid, and serve.

Confit and grilled parsnips with herbs and vinegar

These parsnips are intensely flavoured with vinegar, chilli and smoke from the grill, which adds a wonderful dimension but isn’t strictly essential, so skip the charring stage if you want to save time. Be sure to keep the oil that you’re left with, and use it to dress salads or to drizzle over dips or meze.

Yotam Ottolenghi’s confit and grilled parsnips with herbs and vinegar. Photograph: Louise Hagger/The Guardian. Food styling: Emily Kydd. Prop styling: Louie Waller.

Prep 20 min

Cook 1 hr 20 min

Serves 4-6 as a side

2 red chillies, thinly sliced at a slight angle

3 tbsp apple cider vinegar

Flaked sea salt and black pepper

750g medium parsnips, peeled and halved lengthways

11 garlic cloves, peeled – 10 left whole, 1 crushed

450ml olive oil

4 tbsp coriander leaves, roughly chopped

3 tbsp parsley leaves, roughly chopped

1 tsp ground allspice

Heat the oven to 180C (160C fan)/350F/gas 4. Put the chillies, vinegar and a small pinch of flaked salt in a medium bowl and leave to pickle lightly.

Put the parsnips, whole garlic cloves, oil and a tablespoon of flaked salt in a 30cm x 20cm high-sided baking dish, cover tightly with foil, then roast for an hour, or until a knife slides easily into the thicker part of the parsnips. Use a slotted spoon to lift out the parsnips and garlic, and reserve the oil.

Put a well-greased griddle pan on a high heat and ventilate your kitchen. Once hot, grill the parsnips in two or three batches for about two to three minutes a batch, turning them once, until deeply charred on both sides. Transfer to a large bowl while you continue with the rest. Grill the garlic cloves for a minute, or until charred on both sides, then add to the parsnip bowl.

Put the herbs, crushed garlic, 60ml of the reserved parsnip oil, a quarter-teaspoon of flaked salt and a good grind of pepper in a small food processor and blitz until finely chopped. Stir this and the allspice into the pickled chillies.

Add the herb mixture to the parsnip bowl, tossing gently to combine, then transfer to a large platter, arranging the parsnips cut side up and all pointing in the same direction. Drizzle with two more tablespoons of the parsnip oil and serve warm or at room temperature.