1 tablespoon chopped fresh tarragon, or 1 teaspoon dried
1/4 cup brandy
1/4 teaspoon salt
1/4 teaspoon freshly ground pepper
Preheat oven to 400 °F. Cut 4 pieces of parchment paper or foil about 12 inches by 16 inches each. Fold each in half to get an 8-by-12-inch rectangle, then cut it into a half-heart shape as you would to make a valentine. This is a papillote.
Open the papillotes and place a chicken breast on one half of each opened paper (or foil) heart. Distribute grapes, mushrooms and tarragon over the chicken. Spoon a little brandy over the top and season with salt and pepper. Fold the other half of the heart over to cover the food and bring the edges together. Seal the package by crimping the cut edges together in a series of small, neat folds. Place on a baking sheet.
Bake until the packages are puffed, 10 to 12 minutes. (You may want to open one package to check that the chicken is no longer pink inside.) Transfer to plates and let diners open their own packages.