1. Line 2 large cookie sheets with foil. Using 9-inch cake pan as guide, outline a circle on each cookie sheet; set aside.
2. Prepare meringue: In large bowl, with mixer at high speed, beat egg whites and cream of tartar until soft peaks form; gradually sprinkle in 2 cups sugar, 2 tablespoons at a time, beating well after each addition until sugar completely dissolves and whites stand in stiff, glossy peaks.
3. Preheat oven to 200°F. Spoon meringue into decorating bag with large writing tube. Pipe meringue in concentric circles inside tracing on cookie sheet, making sure there are no spaces between circles. Bake 2 hours. Turn oven off; let meringues remain in oven to dry 1 hour or until crisp. Cool completely on cookie sheets on wire racks.
4. Meanwhile make mocha filling: In 3-quart saucepan over medium heat, heat water, instant coffee, and 3/4 cup sugar to boiling, stirring until sugar dissolves. Set candy thermometer in place and continue cooking, stirring frequently, until temperature reaches 250°F. or hard-ball stage (when a small amount of mixture dropped into very cold water forms a ball that is hard enough to hold its shape). Remove saucepan from heat.
5. In small bowl, with mixer at medium speed, beat egg yolks slightly; beating at medium speed, slowly pour syrup in thin stream into egg yolks. Beat in butter or margarine and chocolate until mixture is very thick, about 10 minutes. Lastly mix in the whipping cream. Refrigerate until mixture is of good spreading consistency but not firm, about 15 minutes.
6. Gently remove meringue layers from cookie sheets. Place 1 layer on cake plate; spread top with half of mocha filling. Top' with second layer and spread with remaining filling. Cover and refrigerate torte at least 3 hours or overnight for easier cutting.