In a large frying pan for which you have a lid, heat the oil over a medium heat until it’s shimmering hot. Add the mustard and fenugreek seeds, leave them to pop for a minute, then add the minced garlic. Stir until the garlic is golden and getting sticky in the pan – this will take a minute, possibly two – then add the tomatoes and a big pinch of salt. Stir to combine, then cover the pan and leave everything to cook on a high heat for five minutes – it should be bubbling fiercely. Add the chilli, ground coriander, cumin, turmeric, tomato puree and a couple of tablespoons of water, if need be to loosen the mixture, cover again and cook for a further two minutes.