Remove the skin from the chicken breasts and halve them. Coat the pieces with the crumbs mixed with the salt, pepper and tarragon. Brown the chicken on all sides in four tablespoons of the butter in a skillet. Place the pieces in a single layer in a shallow baking pan.
Add the onion to the butter left in the skillet and cook until tender. Pour in the stock and wine and bring to a boil. Pour around the chicken. Bake, uncovered, for thirty minutes.
Sauté the mushrooms in the remaining butter and add along with the grapes to the chicken. Bake for eight to ten minutes longer.