Melt the butter with 2 Tbsp. of oil in a heavy-bottomed pot.
Add the chicken, season with salt, and cook until browned. Remove the chicken. It doesn't need to be cooked through - it will simmer a bit.
Add the remaining oil to the pan and sauté the onions until soft. Add the spices and let them bloom, 30-60 seconds.
Sprinkle in the flour and stir until it disappears.
Slowly add the chicken stock and stir, then add the chicken back in. Let it simmer and thicken a bit.
Add the beans, chilies, and cream. Let it simmer to warm through.
Stir in the sour cream just before serving.
