How to Make It
In a very large skillet, heat the oil until shimmering. Lightly season the chicken cutlets with salt and pepper. Add half of the cutlets to the skillet and cook over high heat, turning once, until lightly browned outside and white throughout, about 4 minutes. Transfer the cutlets to a plate. Repeat with the remaining cutlets.
Add the shallot to the skillet and cook over moderate heat until fragrant, about 30 seconds. Add the stock and cook for 30 seconds, scraping up the browned bits. Whisk in the mustard and simmer until the stock has reduced by half, about 3 minutes. Add the olives, currants and capers and simmer over moderately low heat for 1 minute. Return the chicken and any accumulated juices to the skillet and simmer just until warmed through, about 1 minute.
Transfer the chicken to plates. Off the heat, whisk the butter into the sauce until incorporated. Spoon the olive-currant sauce over the chicken cutlets and serve at once.