In a sauté pan, combine the vinegar and sugar. Bring to a boil and reduce until syrupy, coating the back of a spoon.
In a hot non-stick pan, sear the duck breasts—previously scored on the skin side—for 5 minutes skin-side down. Flip and cook 3 minutes more. Season and rest warm in foil.
Pour off the duck fat. Add 15 g butter, melt, and sauté cherries for 2-3 minutes. Add to the vinegar reduction with veal jus; simmer 5 minutes.
Slice the duck breasts. Drain cherries and arrange atop. Just before serving, whisk remaining butter into the sauce for gloss, then coat the duck and cherries.
Serve with small Noirmoutier potatoes boiled in their skins.
Note: Out of season, use frozen or canned cherries.
