Sear the chicken: Heat the oil in a large frying pan over medium-high heat. Season the chicken thighs with a pinch of salt and pepper, then add them to the hot pan in a single layer. Cook for 3-4 minutes per side until the outside is golden brown and you can hear a satisfying sizzle. You're not cooking the chicken through here — just building that deep, savoury flavour. The surface should look caramelised and smell rich and toasty.

Soften the aromatics: Remove the chicken to a plate and add the diced onion to the same pan. Cook for 5-6 minutes, stirring occasionally, until the onion turns translucent and softens. The edges should be just beginning to brown, and the kitchen should smell sweet and fragrant. Add the garlic and ginger and cook for another minute until you can smell their sharp, punchy aroma.

Bloom the spices: Sprinkle the garam masala, cumin, turmeric, chilli powder, and salt over the onions. Stir constantly for 30-60 seconds until the spices become fragrant and the mixture turns a deep, warm amber colour. This step is crucial — raw spices taste dusty and flat, but bloomed spices release their essential oils and taste vibrant.

Build the sauce base: Pour in the crushed tomatoes, chicken stock, and tomato purée. Stir everything together, scraping up any brown bits stuck to the bottom of the pan. These bits are packed with flavour and will enrich your sauce. Let the mixture come to a gentle simmer — you'll see small bubbles breaking the surface and the sauce will thicken slightly.

Combine in the slow cooker: Transfer the sauce to your slow cooker insert. Nestle the seared chicken thighs into the sauce, making sure they're mostly submerged. Add the cubed butter on top — don't stir it in yet, just let it sit on the surface. The butter will melt slowly as the cooker heats up, creating a wonderfully rich, silky texture.

Slow cook: Cover and cook on low for 4-6 hours or on high for 2-3 hours. After about 3 hours on low, the chicken should be tender enough to shred with a fork. The sauce will have darkened to a rich, rusty red and will smell deeply aromatic — like a warm hug in a bowl.

Finish with cream: About 20 minutes before serving, remove the lid and stir in the double cream. The sauce will transform from a deep red to a beautiful, velvety orange-pink. Let it cook uncovered for the final 20 minutes so the sauce thickens slightly. Taste and adjust seasoning if needed — you might want a little more salt or a pinch of sugar if the tomatoes are very acidic.

Rest and serve: Turn off the slow cooker and let the butter chicken rest for 10 minutes before serving. This resting time allows the flavours to meld together and the sauce to settle into its final, luxurious consistency. Garnish with fresh coriander and serve with steamed basmati rice or warm naan bread.