Whisk together the yogurt, lemon juice, turmeric, garam masala and cumin in a large bowl. Put the chicken in, and coat with the marinade. Cover, and refrigerate (for at least 24 hours and up to two days).
Make Sauce
In a large pan over medium heat, melt the butter in the oil until it starts to foam. Add the onions, and cook, stirring frequently, until translucent.
Add the garlic, ginger, and cumin seeds, and cook until the onions start to brown.
Add the cinnamon stick, tomatoes, almonds,chiles and salt, and cook until the chiles are soft, 30 -45 minutes.
Using a food processor or blender, process sauce in batches until completely smooth. Strain through china cap to remove lumps. Return to heat and hold at low simmer until ready to serve.
Roast Chicken
While the sauce is simmering, cover a half sheet pan with foil, put a rack on it, and arrange the chicken so air can circulated completely around each piece. Bake in a preheated oven at 350 until a probe thermometer inserted into the thickest part reads 165*F.
ASSEMBLE
When ready to serve, whisk in the cream, add the roast chicken, and simmer until warmed through and flavors have combined, 10 to 15 minutes.
Garnish with cilantro leaves and serve with Lemon Scented Jasmine Rice