Heat a large skillet over medium-high heat. Add the olive oil and butter and swirl to coat the entire surface of the skillet. Add the chicken, two at a time, and cook approximately 2-3 minutes per side, or until golden brown. If your skillet starts to get smoky, simply lower the heat closer to medium. Remove the chicken from the skillet. Set aside to a wire rack and keep warm in a 200-degree oven. Repeat with remaining chicken.