In a small bowl combine garam masala, ground coriander, sugar, 1 teaspoon salt, ground cumin, turmeric, ground cardamom, white pepper, and ground cinnamon; set aside.
Heat 1/4 cup oil in a large heavy-bottomed pan over medium-low heat. Add the finely chopped onions and 1 teaspoon salt and cook, stirring occasionally, for about 15 minutes until soft and golden brown.
Add the prepared spice mixture to the onions and cook for 1–2 minutes, stirring to coat and bloom the spices.
Stir in the minced garlic and grated ginger, then add the chopped chicken thighs and cook for about 5 minutes, stirring until the chicken is lightly sealed.
Add the tomato passata, almond butter, and 1/4 cup water. Bring to a simmer, cover, and cook on low for 10 minutes; remove the lid and simmer a further 5 minutes.
Stir in the heavy cream and yogurt, cook for 2–3 minutes until heated through and the sauce is combined, then taste and adjust seasoning if needed.
Serve immediately.