Nick Nairn Cook School's Recipe of the Week

SOUP doesn't have to be just a winter warmer.

This light, healthy version is the ideal way to use up the season's crop of courgettes – and give a taste of summer to an elegant dinner party.

If you grow your own courgettes, it's that time of year again – when you wonder what on earth to do with them all. In the Cook School garden, they're coming through thick and fast, but we have the advantage of lots of visitors who are more than happy to cook with and gorge on our freshly grown produce.

This soup is an excellent dinner-party number. Not only can the base be made in advance, but it also dresses up well – that little spoonful of tapenade really seems to impress. If you make it and love it, get a big batch on the go and freeze the base. It will make a good dent on your courgette crop and save a taste of summer for later in the year.

Although courgettes are the main ingredient here, the combination of the parmesan and basil give it a big pesto feel. And be generous with the herbs – the flavour is worth it.

Some places are still available on the Cook School Tapas class on August 19. Visit www.nicknairn.com for further details

Courgette and parmesan soup

For the base

30g unsalted butter

1 small onion, sliced

2 garlic cloves, roughly chopped

500g courgette (about two), topped, tailed and finely diced

600ml chicken stock

To finish

40g fresh herbs (basil, parsley etc), roughly chopped

100g freshly grated parmesan

pinch Maldon sea salt

freshly ground black pepper

To serve

4 tsp tapenade

freshly ground black pepper

finely shaved parmesan

olive oil

basil leaves

To make the soup base, heat a large, thick-based pan on a low to medium heat. Melt the butter in the pan and add the onions. Stir with a heat-proof spatula, then leave to sweat for a few minutes. Watch the pan temperature here; if it gets too hot, the butter may burn and the onions will begin to caramelise and colour. The sound the pan makes is a good indicator of the correct temperature – it should make a very gentle sizzle.

Now add the garlic and stir to combine. Keep the pan on quite a low heat and sweat for a few minutes more.

Meanwhile, prepare the courgettes, trying to keep all the diced pieces roughly the same size.

When the onions have softened and turned a pale golden colour, turn up the heat and toss in the courgettes. Make sure that everything is stirred around. Add the chicken stock and leave the pan to come to the boil – don't add any seasoning at this stage. Then turn down the heat and simmer gently for about ten minutes, or until the courgettes are tender.

To finish the soup, have the tapenade ready. Chop the herbs and add them to the pan with the courgette base. Stir them in and then leave to simmer for about two minutes to infuse the flavours and bring out the vibrancy of the green colour. When ready, the herbs will go nice and dark.

Ladle the soup into a high-speed blender – don't fill it more than three-quarters full. Season with freshly ground black pepper and a pinch of Maldon sea salt. Quickly flick the blender on and off a couple of times to release some of the steam, then switch it on low, gradually turning it up to maximum. Blitz for a couple of minutes; you'll really start to see the colour coming out of the herbs.

Add the parmesan, flick the blender on and off again, then turn on full for a couple of seconds to combine.

Take four serving bowls and half-fill with the soup. Place some parmesan shavings on top of each soup, and then dod a teaspoon of tapenade into the centre. Add a couple of turns of black pepper, drizzle over a little olive oil, and garnish with a sprig of basil. Serve immediately.

Critical points

Not until we started teaching at the school did we realise how much kitchen terminology cooks and chefs take for granted. A novice told us about the last time he'd thought about giving cooking a try. He'd opened the recipe book and read the first line: 'First sweat your onion.' The book was quickly closed and the restaurant promptly booked.

Sweating vegetables means to soften them by cooking slowly over a gentle heat with a little oil or butter. The process releases the sugars in the vegetables, but the gentle heat isn't enough to caramelise them. Do take care not to allow the onions to colour, as the fuller flavour this gives will taint this light soup.

When blending hot liquids, it's not just a case of bunging it in and off you go. To avoid scalds, follow these simple tips. Place all the ingredients in the jug and put the lid on. Take out the central cup from the lid to allow steam to escape. If you leave it in, the lid is sealed and creates a dangerous build-up of steam.

Never fill a blender more than three-quarters full. Use a clean tea towel to completely cover the hole – this will prevent splattering and will let some of the steam escape while processing. Finally, give the mixture a couple of quick pulses to allow more steam out. You're now ready for the big blitz.