Meanwhile, heat a medium skillet until very hot. Sprinkle the sugar in the skillet and cook over moderate heat until caramelized, about 20 seconds. Add the verjus and cook for 10 seconds. Add the Syrah and cook, shaking the pan frequently, until the sugar dissolves and the wine is reduced by half, about 10 minutes. Stir in the demiglace, stock and rosemary sprig and simmer over moderate heat until reduced to 1 cup, about 15 minutes. Add the dried cherries and simmer over low heat just until softened, about 5 minutes. Season lightly with salt and pepper. Discard the rosemary sprig and transfer the sauce to a warmed gravy boat.