Beetroot and celeriac gratin (V)

Just right for the season – warm, comforting and colourful. Either boil or roast the beetroots. Serves six.

500ml double cream

1 medium onion, peeled and quartered

20g thyme sprigs, leaves picked but also keep the stems

2 bay leaves

6 cloves garlic, peeled and lightly crushed

Shaved skin of 1 large lemon

8 whole cloves

Salt and white pepper

4-5 medium beetroots (700g), boiled, peeled and sliced 2mm thick

1 large 900g celeriac, peeled and sliced widthways 2mm thick

100g hard mozzarella, grated

150g extra mature cheddar, grated

Heat the oven to 180C/350F/gas mark 4. Pour the cream into a medium saucepan and add the onion, thyme stems, bay, garlic, lemon skin, cloves, a teaspoon of salt and a teaspoon of white pepper. Gently bring the cream to a boil, then remove from the heat. Set aside to infuse for at least 10 minutes, then strain.

Scatter a third of the beetroot and celeriac on the base of a 27cm x 18cm baking dish or high-sided roasting tray. Pour over a few spoonfuls of cream and sprinkle a third of the cheese and thyme leaves on top. Arrange another layer of vegetables followed by a little cream and another third of the cheese and thyme. Place the final layer of vegetables on top, pour over the remaining cream, holding back the last of the cheese and thyme leaves, and gently press down to level.

Cover with foil and bake for 50 minutes. Reduce the temperature to 160C/320F/gas mark 2½, remove the foil and bake for 20 minutes more. Sprinkle over the last of the cheese and thyme, and bake for another 15 minutes, until the cheese is golden brown and the vegetables are cooked through. Leave to sit in a warm place for five to 10 minutes before serving.

Scrambled eggs with merguez and preserved lemon

Tunisia, a country of which I knew very little before last summer, was another stop on my Mediterranean journey for More 4. I was bowled over by the deft and complex use of spices, and by this gutsy, spicy cuisine which isn't shy of using lots of components in one dish, all loud, all colourful and all competing for attention. Cumin is a key spice, as is caraway, while aniseed surprised me by its popularity. Aniseed or fennel seed is also a key spice in the local merguez sausages. Serves four.

1 tbsp olive oil

1 small onion, peeled, thinly sliced

200g charlotte potatoes, peeled and sliced ½cm thick

150g merguez sausages, sliced on an angle 1cm thick

2 cloves garlic, thinly sliced

1 tsp caraway seeds

½ tsp ground turmeric

2 tsp harissa paste

½ tsp tomato paste

8 medium eggs

50ml double cream

Salt and pepper

10g preserved lemon, flesh and skin, finely chopped

2 tbsp chopped coriander or parsley

Put a large sauté pan on a medium to high heat, add the oil and cook the onion for five minutes to soften. Add the potato, sausage, garlic, caraway, turmeric, harissa and tomato paste, and fry for two minutes. Pour over 100ml water and simmer for eight minutes, until the potato and sausage are cooked and the water has evaporated (add a little more water if you need to cook it longer).

Whisk the eggs and cream with a quarter-teaspoon each of salt and pepper. Pour the eggs over the hot potato mix, reduce the heat to low and gently stir until just cooked. Stir through the preserved lemon, taste for seasoning and serve sprinkled with coriander or parsley.

• Yotam Ottolenghi is chef/patron of Ottolenghi and Nopi in London. His new book, Jerusalem, co-written with Sami Tamimi, is published by Ebury Press at £27. To order a copy for £16 (inc free UK mainland p&p), go to theguardian.com/bookshop, or call 0330 333 6846.

The new Ottolenghi app is available now on iTunes for £4.99.