Prepare a campfire for cooking or set your camp stove for medium heat.
Add the butter and oil to a large Dutch oven and set over the heat.
When the butter is melted, stir in the onion and sauté until softened, about 8 minutes.
Stir in the garlic and ginger, and cook until fragrant, about 30 seconds.
Add 1 teaspoon garam masala, the chili powder, cumin, and coriander, and cook for 30 seconds more, stirring constantly.
Pour in the passata and cream and bring the mixture to a simmer.
Season the chicken all over with salt, pepper, and the remaining 1 teaspoon garam masala.
Stir in the chicken, cover the Dutch oven and simmer until the chicken is cooked through and the flavors have come together, 15 to 20 minutes. Season to taste with salt and pepper and serve immediately.