Preheat oven to 350ºF. Grease and lightly flour a 9” round cake pan; line bottom with wax paper.
Microwace 3 squares of the chocolate and butter in a large microwaveable bowl on high 1-1/2 to 2 minutes or until chocolate is almost melted, stirring after 1 minute. Stir until chocolate is completely melted. Stir dry gelatin mix and sugar into chocolate until well blended. Mix in eggs. Stir in flour and nuts until well blended. Pour into prepared pan.
Bake 40 minutes or until toothpick inserted in center comes out with moist crumbs. Do not overbake. Cool in pan 5 minutes. Run a small knife around side of pan to loosen edge. Invert onto a serving platter; remove wax paper. Cool cake completely.
Meanwhile melt remaining 4 squares of chocolate in large microwaveable bowl on high 1-1/2 minutes or until melted; stirring afer 1 minute. Stir until chocolate is completely melted; stir in whipped topping until smooth. Frost cake with whipped chocolate mixture. Lightly dust with confectioners sugar before serving.