Roughly chop 1 large onion, transfer to a small food processor, and add 3 tbsp of water - process to a slack paste. You could use a stick blender for this or coarsely grate the onion into a bowl – there’s no need to add any water if you are grating the onion. Tip into a small bowl and leave on one side.
Put 6 roughly chopped garlic cloves and 50g roughly chopped ginger into the same food processor and add 4 tbsp water – process until smooth and spoon into another small bowl. Alternatively, crush the garlic to a paste with a knife or garlic press and finely grate the ginger.
Heat 4 tbsp vegetable oil in a wok or sturdy pan set over a medium heat.
Combine 2 tsp cumin seeds and 1 tsp fennel seeds with a 5cm cinnamon stick and 1 tsp chilli flakes and add to the pan in one go. Swirl everything around for about 30 secs until the spices release a fragrant aroma.
Add the onion paste – it will splutter in the beginning. Fry until the water evaporates and the onions turn a lovely dark golden - this should take about 7-8 mins.
Add the garlic and ginger paste and cook for another 2 mins – stirring all the time.
Stir in 1 tsp garam masala, 1 tsp turmeric, and 1 tsp caster sugar and continue cooking for 20 secs before tipping in a 400g can chopped tomatoes.
Continue cooking on a medium heat for about 10 mins without a lid until the tomatoes reduce and darken.
Cut 8 skinless, boneless chicken thighs into 3cm chunks and add to the pan once the tomatoes have thickened to a paste.
Cook for 5 mins to coat the chicken in the masala and seal in the juices, and then pour over 250ml hot chicken stock.
Simmer for 8-10 mins without a lid until the chicken is tender and the masala lightly thickened – you might need to add an extra ladleful of stock or water if the curry needs it.
Sprinkle with 2 tbsp chopped coriander and serve with Indian flatbreads or fluffy basmati rice and a pot of yogurt on the side.
