Wash 175g of small red lentils in cold running water. Put 1 tsp of cumin seeds in a spice grinder. Crack 8 cardamom pods, extract the black seeds from within and add them to the cumin. Grind the spices to a coarse powder. (You can also do this with a pestle and mortar.) Tip the ground spices into a food processor, then add 35g of ginger, peeled and cut into pieces, 3 cloves of garlic, peeled, 1 tsp of turmeric powder and 2 small chillies. Pour in 1 tbsp of groundnut oil and process to a coarse paste.
Pour 2 tbsp of oil into a deep saucepan over a moderate heat, add 1 tsp of yellow mustard seeds and let them cook for a minute, Stir in the spice paste and fry for a minute or two until fragrant. Stir in 1 tbsp of tomato purée. Chop 250g of tomatoes and add to the pan, continue cooking for a few minutes then, as the tomatoes soften and collapse, add the lentils, drained of their water, 3 tsp of tamarind paste, 750ml of water and a ½ tsp of salt. Lower the heat and leave to simmer for 25 minutes. Enough for 4
When frying the mustard seeds they may start to pop and jump out of the pan. Keep the heat low, which will discourage this, and have a lid handy to limit their trajectory. Stir the soup regularly throughout cooking as the lentils tend to fall to the bottom of the pan and will catch and burn.
Use less liquid, or reduce the content by simmering for a while longer than the recipe suggests, and use the resulting spicy, tomatoey lentil sauce to have over rice. Ideally it will be brown basmati, perhaps finished with a little yoghurt and a few chopped mint leaves.