In a medium saucepan with a tight-fitting lid, combine the mint sprigs, rosemary, verjus, sugar, and salt. Bring just to a boil. Set aside, covered, to steep until the herbs flavor the liquid, about 30 minutes. Strain the liquid and discard the herbs. Pour 1/4 cup of the infused liquid into a bowl, sprinkle the gelatin over the surface and set aside to let it "bloom" for about 5 minutes. Reheat the remaining liquid and whisk it into the gelatin mixture until evenly dissolved.
Pour the verjus mixture into a small gratin dish and refrigerate until thickened and almost set about, 20 minutes. Chiffonade the mint leaves, and stir into the aspic. Refrigerate until set, about 30 minutes more.
Yield: about 1 1/2 cups