Remove the bones from the bone-in thighs as needed, then cut all of the chicken into bite-sized pieces, keeping the skin on any pieces that already have it. Uniform pieces cook more evenly, and the skin adds extra richness as the curry slowly cooks.

Place the chicken in the slow cooker and grate the fresh ginger directly over the top. The ginger should smell bright and sharp right away, which is a good sign it will carry through the creamy sauce.

Sprinkle in the garam masala, kosher salt, onion powder, and smoked paprika, then stir to coat the chicken well. Once mixed, the chicken should look evenly stained with spice and smell warm and fragrant.

Add the canned diced tomatoes, minced garlic, olive oil, and tomato paste, then stir again until the mixture is well combined. The tomato paste should disappear into the mixture instead of sitting in dense streaks.

Pour in half of the coconut milk and mix thoroughly, then cook on low for 6 hours or on high for 3 hours. By the end, the chicken should be very tender and the sauce should look darker, looser, and fully aromatic.

Stir in the remaining coconut milk, the heavy whipping cream, and the guar gum after the cooking time is finished, then mix until the sauce thickens. The curry should turn creamy and smooth, with a sauce that lightly coats the chicken instead of running thin.