Combine garam masala, ground coriander, sugar, 1 teaspoon salt, ground cumin, turmeric, ground cardamom, white pepper, and ground cinnamon in a small bowl; set aside.
Heat oil in a large heavy-bottomed pan over medium-low heat. Add the chopped onions and the remaining 1 teaspoon salt and cook, stirring occasionally, until soft and golden brown, about 15 minutes.
Add the prepared spice mixture to the onions and stir to coat evenly, cooking 1–2 minutes until fragrant.
Stir in the minced garlic and grated ginger, then add the chopped chicken thighs. Cook, stirring, for about 5 minutes until the chicken starts to brown.
Add the tomato passata, almond butter, and water; stir to combine and bring to a simmer. Cover and cook on low for 10 minutes, then remove the lid and simmer for 5 more minutes.
Stir in the heavy cream and yogurt, cook for 3 minutes until heated through and the sauce is smooth.
Taste and adjust seasoning if needed, then serve.
