Heat 1 tablespoon of the oil in a sauté pan over medium heat; add the chicken breasts or thighs and brown for about 3 minutes per side until the chicken turns opaque.
Remove and place the chicken in an ovenproof casserole dish or Dutch oven.
Add the remaining oil, butter, and onion to the sauté pan; sauté until onion is wilted, about 5 minutes.
Add the garlic, cardamom, coriander, black pepper and blanched sliced almonds; cook until the nuts are pale gold, about 3 minutes.
Transfer the onion mixture to a blender (or food processor, but a blender will work a little better); add the yogurt or sour cream and puree until smooth.
Season the sauce with salt to taste and pour over the chicken pieces in the casserole dish.
Bake at 350 degrees for 50 minutes, or until the chicken is tender and juices run clear.
Garnish with toasted almonds and serve with the sauce and rice.
Note: if you've not made this dish before, I recommend starting with 1 teaspoon of cardamom; taste it when you season to taste with salt before pouring over the chicken to bake, and add more cardamom if you like.