In a mixing bowl, combine plain yoghurt, minced garlic, freshly grated ginger, garam masala, salt, cumin, paprika, vegetable oil, cayenne pepper, and lemon juice. Add the chicken thighs, ensuring each piece is well-coated. Cover and refrigerate for a minimum of 3 hours or preferably overnight.

Heat a non-stick pan over high heat until smoking. Add 2-3 tablespoons of vegetable oil to coat the bottom. Once hot, add half the marinated chicken and sear for 2-3 minutes on each side until charred. Remove and repeat with remaining chicken.

In the same pan, reduce the heat to medium and add 3 tablespoons of butter or ghee. Sauté the onion and a teaspoon of ginger until golden brown, about 5-7 minutes. Stir in minced garlic and paprika, cooking for an additional 2 minutes.

Sprinkle in turmeric, garam masala, coriander, cumin, and optional cayenne pepper. Stir for 1-2 minutes until fragrant. Pour in the tomato passata and 100ml of water, mix well. Bring to a gentle simmer, cover, and reduce heat for 15 minutes.

Transfer the sauce to a blender and puree until smooth. Return the blended sauce to the skillet, scraping down flavorful bits. This step is crucial for the authentic finish.

Add the cooked chicken back to the sauce along with cream, sugar, and an additional tablespoon of butter. Stir and let simmer on low for 5-10 minutes until heated through. Adjust seasoning to taste.

Serve over basmati rice or with naan bread. Garnish with fresh coriander if desired. Enjoy your Chicken Tikka Masala!