Mix salt, paprika, garam masala, cumin, coriander, cayenne, and turmeric together in a small bowl. Set spice mix aside.

Cut one chicken thigh in half lengthwise along the crease. Halve the thicker portion to end up with three 2-inch pieces. Repeat with the remaining chicken thighs.

Transfer chicken to a bowl. Add oil and about 1/2 of the spice blend; mix thoroughly. Cover with plastic wrap and marinate in the refrigerator for 4 to 12 hours.

When ready to cook, heat 1 tablespoon butter in a large pan over high heat until melted and golden brown. Add chicken in a single layer and cook until browned, 4 to 5 minutes per side. Return chicken and any accumulated juices to the bowl.

Heat remaining butter in the same pan over medium-high heat. Add onion, garlic, tomato paste, ginger, and the remaining spice blend. Cook and stir until fragrant, 2 to 3 minutes. Pour in chicken broth and bring to a simmer. Add chicken and any accumulated juices.

Combine water and cashews in a blender; blend on high speed until very smooth, then stir into the pan. Reduce the heat to medium and simmer until flavors blend, 15 to 20 minutes. Stir in green onions and cilantro; taste for seasoning. Squeeze in lime juice.