Drizzle the chicken with the oil and sprinkle on the garam masala, curry powder, salt and pepper.
Massage into the meat and cover, leaving to marinate for at least 2 hours or overnight.
Heat a grill pan over medium-high heat. Grill the chicken for 5-6 minutes per side, until cooked through.
Meanwhile, make the korma sauce: place the onions, garlic, and 1 cup of water in the bowl of a blender.
Puree until smooth.
Measure out the spices (curry powder through nutmeg) into a small bowl.
In a large saucepan heat 3 tablespoons of olive oil over medium heat. Once the oil is shimmering, add the pureed onion mixture and cook for a 2-3 minutes, stirring constantly, until it begins to darken in color.
Add the tomatoes, ginger, ground almonds, coconut milk, yogurt, red chili, pre-measured spices, and brown sugar. Stir well.
Turn the heat down to low and simmer 30 minutes.
Cut the chicken into bite-sized pieces and add to the pan; simmer for an additional 15 minutes.
Serve with steamed basmati rice and/or naan