Peel and chop the onion or trim, rinse and shred the leek into small pieces. Peel and chop the carrot into small dice. Rinse and finely chop the celery or red pepper (whichever you're using)
Heat a couple of tablespoons of water in the base of a large pan and add the chopped vegetables. Sauté for 5-8 minutes until they start to soften, add more water if needed to stop them sticking to the base of the pan.
Stir in the lentils, tinned tomatoes, smoked paprika, thyme and chilli flakes if using. Cook for a minute. Add the stock, stir well and bring to the boil.
Reduce the heat and simmer for 20 minutes or so until the lentils are swollen and cooked.
Leave to cool for a few minutes, then blend until smooth. Season with salt and pepper to taste.
Serve hot with a garnish off fresh coriander if desired.
