Cube chicken meat and 3 oz of the shrimps and chill. Purée in a food processor. Add salt and pepper. Add egg whites and brandy and mix well. Slowly add heavy cream.
Dice remaining shrimps, truffle, and mushrooms. Peel pistachio nuts and mix into forcemeat. Hollow tomatoes carefully, starting with stem, and fill with forcemeat. Cover tightly with plastic wrap and aluminum foil. Set on a wire rack over some water. Cover and steam at 175° to 180°F for 25 minutes.
Remove plastic wrap and aluminum foil; remove tomato skin. Chill. Glaze with lemon aspic jelly. Garnish with tournéed marinated cucumbers and New Orleans Sauce (see below).