In a large skillet, brown the cutlets on both sides, two at a time in half the butter. Season with salt and pepper. Set aside on a warm plate.
In the same skillet, sauté the onions in the remaining butter. Sprinkle with the flour and stir to combine. Deglaze the hot skillet with the wine and bring to a boil, while stirring. Add the remaining ingredients. Bring to a boil and reduce by half. Adjust the seasoning.