In a large bowl, whisk together the yogurt, ginger garlic paste, lemon juice, Kashmiri chilli powder, ground coriander, and salt. Add the chicken chunks and toss until every piece is well coated. Cover and refrigerate for at least 30 minutes — this short marinade is what keeps the chicken juicy through the long slow cook.

Heat the ghee in a large skillet over medium heat. Add the sliced onions and cook for 8–10 minutes, stirring often, until deep golden brown at the edges — not just soft, properly caramelised. Stir in the ginger garlic paste, fresh red chillies, cardamom pods, cloves, cinnamon stick, and bay leaves; cook 1 minute until fragrant. Add the Kashmiri chilli powder, turmeric, cumin, coriander, and half the garam masala; stir 30 seconds until the spices darken a shade and smell incredible.

Pour in the passata and add the cherry tomatoes and salt. Simmer for 5–6 minutes until the tomatoes slump and the oil starts to glisten at the edges — that's the sign the base is ready. Blend the soaked cashews with a splash of warm water into a smooth paste and stir it through; this is what gives rogan josh its luxurious, slightly thickened sauce.

Transfer everything to your slow cooker. Add the marinated chicken along with all its marinade and stir to coat. Pour in the warm water if it looks thick — you want a rich sauce, not a soup. Cover and cook on high for 3 hours or low for 5–6 hours, until the chicken is completely tender and the sauce is a deep, glossy red.

Fish out the whole spices you can find (cinnamon stick, bay leaves, cardamom pods). Stir in the remaining garam masala and let it sit for 10 minutes with the lid off so the sauce thickens slightly. Taste and adjust the salt — the long cook mellows everything, so it often needs one final pinch.

Spoon into warm bowls, drizzle with yogurt, and shower with fresh coriander. Serve with basmati rice or naan to soak up every drop of that red sauce.