1. In a skillet heat the butter, add the duck and brown on all sides. Drain off the fat. Pour the sherry over the duck and remove it to a platter.
2. To the pan add the garlic and cherries, reserving the juice. Boil two or three minutes. Blend the potato flour with the reserved cherry juice and tomato paste and add, stirring, to the cherries. Cook, stirring, until thickened. The sauce should have the consistency of heavy cream. If too thick, thin with chicken broth.
3. Return the duck to the pan, skin side down. Add the bay leaf, cover with waxed paper and skillet lid and simmer until done, forty to fifty minutes. Arrange the duck on a platter and garnish with the cherries.