Cream butter in medium-size bowl and gradually add sugar, creaming well after each addition.
Cool melted chocolate; blend into butter-sugar mixture with instant coffee and vanilla.
Add eggs, one at a time, beating VERY WELL after each addition. (Use an electric beater or mixer, for you'll need to beat in each egg 5 minutes to make mixture creamy, thick, and fluffy.)
Turn into baked pastry shell; chill 1 - 2 hours. Just before serving, whip cream and garnish pie.
