Put the chicken in a mixing bowl. Add the yoghurt, Garlic and Ginger Paste, lemon juice, Kashmiri chilli powder, Garam Masala, cumin, salt and rapeseed oil. Mix thoroughly, cover and refrigerate for at least 2 hours or overnight.

Melt 25g butter with 15ml rapeseed oil in a saucepan over a medium heat. Add the Garlic and Ginger Paste and cook for 45 seconds, stirring continuously.

Add the Kashmiri chilli powder and ground coriander. Stir for 15 seconds, then add the plum tomatoes, cashews, salt and 150ml hot water. Break up the tomatoes with a spoon, bring to a simmer and cook uncovered for 20 minutes, stirring occasionally.

Preheat the grill to high and line a sturdy metal tray with foil. Arrange the marinated chicken in a single layer and grill for 12 to 16 minutes, turning halfway, until lightly charred and cooked through. The centre should reach 75°C for 30 seconds, or be steaming hot with no pink meat.

Remove the tomato mixture from the heat and blend until completely smooth. Pass the sauce through a fine sieve into a clean saucepan, pressing it through with the back of a ladle and discarding the coarse residue.

Return the sauce to a low heat. If necessary, add hot water a little at a time until it is thick but pourable. Simmer gently for 3 minutes.

Stir in the double cream, remaining 25g butter, Garam Masala and dried fenugreek leaves, crushing the leaves between your fingers as you add them. Simmer gently for 2 minutes.

Add the grilled chicken and any juices from the tray. Simmer gently for 4 to 5 minutes, until piping hot and coated in the sauce. Taste and add the optional sugar only if the tomatoes remain too sharp. Adjust the salt and serve.