1. To prepare the sauce base, melt the butter with 1 tablespoon of the oil in a large non-stick frying pan. You need a pan with a lid but if you don’t have one handy, use a large non-stick saucepan instead. Add the onions to the pan, then cover with a lid and cook over a low heat for 15 minutes until very soft, stirring occasionally.

2. Remove the lid from the pan and turn up the heat. Cook the onion mixture for 2-3 minutes more, stirring constantly until well coloured. Add the curry paste, cinnamon and cardamom to the pan, turn down the heat slightly and cook with the onions for 3 minutes more, stirring frequently. Add a little water if the mixture gets too dry. Remove the pan from the heat and stir in the tomato purée.

3. Blitz the spiced onions with a stick blender or tip them into a food processor and blend until as smooth as possible. Tip the onion mixture into a bowl and set aside. If you want to, you can keep the mixture covered in the fridge for up to 3 days.

4. Place the pan used to cook the onion mixture back over a medium heat and add the remaining oil and the chicken pieces. Fry the chicken for 3 minutes, turning often until lightly coloured all over. You can do this in two batches. Put the chicken aside.  Heat the remaining oil, add peppers and stir-fry until edges slightly browned.

5. Add the chicken and all the spiced onion mixture, 185ml just-boiled water, salt, and tomatoes, bring to a simmer and cook for 4 minutes. Add the spinach in a few handfuls, allowing each to soften a little before adding the next. Cook for a further minute, stirring regularly, or until the chicken is cooked through, the tomatoes are softened and the spinach has wilted. Stir in the fresh cream and lime juice, warm through and it’s ready to serve with boiled rice or/and naan bread.