n a large pan, melt butter or ghee over medium heat. Add diced onion and sauté until translucent.
Add garlic paste, ginger paste, and spices (coriander, garam masala, cumin) and cook until fragrant.
Stir in the passata or diced tomatoes and heavy cream. Mix well.
Add cashews and simmer for 5 minutes.
Transfer the mixture to a blender or food processor and blend until smooth. Add hot water to adjust consistency.
Strain the blended sauce back into the pot to ensure a silky texture. Simmer gently, adjusting seasoning as needed.