Preheat oven to 350 degrees F (175 degrees C). Grease and flour a 9x13 inch pan.
In a large saucepan combine the non-instant pudding mix with 2 cups milk. Cook over medium heat, stirring constantly, until the pudding is thickened. Remove from heat. Pour the dry cake mix into the saucepan and mix until smooth. Pour batter into prepared pan and sprinkle with chocolate chips and walnuts.
Bake in the preheated oven for 20 to 30 minutes, or until a toothpick inserted into the center of the cake comes out clean.