Heat a large skillet or pot over medium-high heat. Whisk together the sugar, paprika, garlic powder, onion powder, cumin, chili powder, ground mustard, salt and pepper. Rub it all over the chicken. Add the olive oil and butter to the skillet. Place the chicken in the oil once hot and brown on both sides until deeply golden, about 3 to 4 minutes per side. I sometimes cover the skillet while doing this and it helps cook the chicken through.