By hand, add flour, frosting mix and walnuts. Stir until mixture is smooth. Batter will be thick. Spoon batter into a greased and floured bundt pan. Bake 55 minutes.
Timing is important.
Top will be shinny. Cool 2 hours. Turn pan over onto cake plate. The inside of the cake will form a tunnel of fudge. Serve plain or topped with vanilla ice cream or Cool Whip with chocolate syrup.