How to make a zingy ketchup from overripe tomatoes | Waste not

I’ve been developing today’s recipe for almost 20 years, since setting up my festival cafe, Poco, in 2004. Over the years, the recipe has evolved. Now we ferment it, which keeps it safe to eat without refrigeration – a limited resource in a field kitchen. As well as preserving the food, lacto-fermentation has also had the benefit of improving the flavour, adding complexity and umaminess.

This recipe is an effective way of preserving a glut of super-ripe, extra-flavourful tomatoes, or turning unripe, flavourless tomatoes into something delicious. Now they are in season, keep your eyes peeled for bargain bags of ripe tomatoes at the market.

Lacto-fermented harissa ketchup

Harissa is delicious, but super spicy. This is my version, which is made with squishy, ripe tomatoes to soften the heat and allow generous application. We serve it at Poco Cafe on a slow-roast lamb kebab and in a halloumi wrap. It’s also lovely with brunch, or almost any dish you fancy a little spicy ketchup on. It’s a great way to preserve a glut of super-ripe tomatoes or to turn flavourless unripe tomatoes into something very flavourful. Add between 100 and 200g chillies, depending on whether you prefer a mild or medium-hot sauce. I usually make a mild sauce with 100g chillies, then add extra chilli flakes to a dish if I want additional heat.

Makes About 900g

2 tbsp extra-virgin olive oil
1 small red onion (about 70g), roughly chopped
4 large garlic cloves, peeled
2 tbsp cider vinegar
2½ tsp sea salt
2 tsp sugar
2 tsp cumin seeds
2 tsp smoked paprika
2 tsp caraway seeds
1kg very ripe tomatoes, roughly chopped
100g or 200g red chillies (for a mild or medium hot sauce)
1 red bell pepper (about 150g)

Put the oil in a saucepan on a medium heat. Add the onion and saute, stirring, for five minutes. Add the whole garlic cloves, along with the vinegar, salt, sugar, cumin, smoked paprika and caraway, then fry, stirring, for two minutes more. Add the tomatoes, bring to a boil, then turn down to a simmer and cook for 15 minutes, or until reduced by a third.

Meanwhile, in a dry frying pan, blacken the chillies and whole bell pepper . Once charred on one side, turn and char another. Repeat until blistered all over and softened.

Pluck off and compost the stalks, then put all the chillies and pepper in a blender with the spiced tomatoes. Pulse blend into an even but textured sauce. Transfer into clean bottles or jars, with the lids loosely placed on top. Leave at room temperature to ferment for four to 14 days, or until bubbles begin to form. Keep in a cool, dark cupboard or fridge for three to six months.