Heat a large saucepan over medium-high heat and, once hot, drizzle in the oil, reduce the heat to low and cook the finely chopped onions until golden brown. Season.
Add the ginger and garlic purée, curry powder, turmeric, chilli powder, 1 tsp fine salt and a splash of water, and stir well. Fry for a couple of minutes, then add the diced chicken thighs and stir well again.
Mix the yogurt, tomato purée and onion purée together in a jug with 300ml water. Pour into the saucepan and mix well. Turn up the heat and bring to the boil, then reduce the heat and simmer for 15-20 mins, stirring occasionally. Sprinkle in the garam masala for the final 2 mins of cooking, stir well and serve.
Mix the yogurt, tomato purée and onion purée together in a jug with 300ml water. Pour into the saucepan and mix well. Turn up the heat until the sauce begins to boil. Simmer for 15 to 20 mins, stirring occasionally.
Finally, sprinkle in the garam masala and stir in well for the final 2 mins before serving.
