In a small saute pan over medium heat, toast the cashews, coriander, cumin, red pepper flakes, and peppercorns until fragrant, about 2 minutes.
Crush the toasted spices in a mortar and pestle, coffee grinder or mini food processor until finely ground. Mix in the garam masala.
Rub the spice mixture into the chicken thighs. Let them rest for 3 to 4 minutes.
Heat a large, high-sided pan over medium-high heat. Spray the pan evenly with cooking spray. Sear for 2 minutes on each side. Turn off heat and transfer the chicken to a plate.
Add the tomatoes, red onion, ½ cup water, ginger, garlic and chile. Turn the heat back on and stir to deglaze. Simmer for 30 minutes, covered, over low heat.
While the sauce is simmering, in a separate saucepan make a beurre fondue cream sauce. Heat ½ cup water to about 190° (bubbles form on the bottom of the pot, but no boiling takes place.) Turn off the heat and whisk in the butter followed by the creme frache. Let stand for one minute.
After the tomato sauce has simmer for 30 minutes, pour the tomato sauce into the blender and pulse until the sauce is smooth. Add the cream sauce and blend for another minute or two.
Put the sauce back in the braising pan and add the chicken thighs. Cook over low heat for about 30 minutes until the chicken is tender.
Serve over rice with homemade or store-bought naan.