Combine Spice mix and use a little more than half to marinade the chicken, and the rest to add to the sauce.
Cut chicken thighs into quarters. Combine chicken with 1 tablespoon vegetable oil and spice blend, and marinated for 4 to 12 hours.
Melt butter over medium high heat and add chicken to pan in a single layer. Cook in two batches rather than crowd the pan. Sear for 4-5 minutes on both sides and set aside.
Return pan to medium-heat and add butter, onion, leftover spice, tomato paste, garlic and ginger. Cook stirring for five minutes and add chicken stock. Bring to a boil and return chicken to pan.
Add cashews and water to a blender and blend on high. Add to pan. Reduce heat to medium and reduce sauce for 20-30 minutes.