Wash the chicken fillets & pat dry. Cover with waxed paper & flatten slightly with a meat mallet. Set chicken aside. In a small saucepan melt butter & saute walnuts & chives for 5 minutes. Remove pan from heat & stir in tarragon, cream, brandy & pepper. Peel & quarter mango. Place the mango sections in a buttered baking dish. Liberally coat each section with the walnut herb stuffing. Carefully lay a chicken fillet over each mango section & mold into a mound. Brush with lemon juice. Roll out the chilled pastry to 1/8" thick & cut to cover each chicken fillet as neatly as possible. Trim off any excess pastry. Bake chicken at 350 for 1 hour.
