Place chicken thigh pieces in a mixing bowl, add 1 ½ teaspoons cumin, ½ teaspoon coriander, a sprinkle of salt, and some cracked black pepper and toss together until chicken is well coated.
Place a large skillet over medium-high heat and add 1 ½ tablespoons butter.
Add chicken and sauté for 3 to 4 minutes.
Using a slotted spoon, transfer chicken to a plate and set aside.
Add remaining butter to skillet. Add shallot and garlic and sauté 3 to 4 minutes.
Add cashews and remaining spices and continue to sauté for an additional 4 to 5 minutes. Season with salt and pepper.
Transfer mixture into a blender with 1 ¾ cups water and blend until smooth.
Pour mixture back into skillet, stir in tomato paste and simmer over medium-low heat for 2 to 3 minutes.
Pour chicken into skillet with korma sauce and stir together. Simmer mixture until slightly thickened. Season with salt and pepper and stir.
Pour chicken korma over a bed of buttery, mashed potatoes and top with fresh cilantro leaves. Serve.