This soup is slow Mexican food at its glorious best. It’s based on a deeply flavoured roast vegetable stock, which whilst taking around 2 hours to make, is worth it and you get 500ml left over for next time (or other dishes). We've also discovered that it works well with 500ml vegetable nage and 500ml roast stock. You could substitute our more conventional non-baked vegetable nage to save time, but it won’t be quite the same. The soup has a deep, rich beany flavour with a dark gentle hint of chocolate; use the best quality dark chocolate that you can get your hands on, its sits behind the main flavours, but you’d really miss it if it wasn’t there. Chocolate tends to disappear when you reheat frozen savoury dishes so you may need to top it up. The salsa is served at the bottom of the soup, so you get a flavour hit when you dig your spoon into the bowl.

Roast vegetable stock:- (makes 1.5 litres)

6 sprigs fresh flat-leaf parsley

6 sprigs fresh thyme

6 medium carrots, peeled cut into 2.5cm pieces

4 medium celery sticks, cut into 2.5 cm pieces

1 large onion, peeled and cut into 8 wedges

½ head of garlic (optional), peeled and lightly bashed

1 medium red onion, peeled and cut into 8 wedges

2 tbspns groundnut oil

2 large bay leaves

225 ml dry white wine

The soup:-

2 tbspns olive oil

2 red onions, finely chopped

3 tablespoon chives, finely chopped

2 fresh hot red chillies, deseeded if you prefer, and finely chopped

1 chipotle chilli, finely chopped (not optional)

1 tspn dried oregano

1 tspn ground coriander

1 tsp ground allspice

2 sticks of celery, finely chopped

½ red pepper deseeded and finely chopped

800g drained tinned black (turtle) beans (4 tins)

1 tbspn tomato purée

1 litre roasted vegetable stock (see above)

30g dark chocolate, finely chopped

For the avocado salsa:-

1 avocado, peeled, stoned and diced

1 tbsp chopped fresh coriander

Juice of 1 lime

To serve:-

Best quality tortilla chips (or home made)

100g Feta cheese, finely crumbled or Queso Fresco

To make the veg stock:-

• Position a rack in the center of the oven and heat the oven to 220C

• In a large roasting pan, toss the herb sprigs, carrots, celery, garlic (if using) and onions with the oil and a few grinds of black pepper. Spread into a snug single layer. Roast, stirring twice, until the vegetables are tender and browned in spots, for about 40 minutes

• Transfer everything to a stock pan or large wok, add 2.8 litres cold water and the bay leaves, and bring to a boil. Turn the heat down and simmer gently, uncovered, for 30 minutes

• Add the wine and simmer for 20 to 30 until the broth is reduced by about one-third to 1500ml and has a full vegetable flavour. Strain the broth through a fine-mesh sieve, pressing gently on the vegetables to extract as much liquid as possible. Discard the solids. Season well and set aside

To make the soup:-

• Heat the olive oil in a large, heavy saucepan, and sauté the onions for eight minutes over a medium heat. Add the chives, chillies, oregano, ground spices, red pepper and celery, and cook for seven to eight minutes more, until the vegetables are soft, but not browning. Add the beans, tomato purée and stock, bring to the boil, then cover and simmer for 40 minutes

• Make the salsa by combining all the ingredients in a bowl

• Use a blender to make a smooth purée of the soup. Add the chocolate and season with salt – it will need quite a bit

• To serve, put a couple of teaspoons of the avocado mix at bottom of each bowl. Add the soup then top with 4-5 tortilla chips and the crumbled feta cheese