To prepare cake:
Prepare cake mix according to package directions, adding the additional flour as you mix. Bake in two 9" round cake pans. Once cool, split each cake round in two to form 4 cake layers.
To prepare filling:
Blend milk into flour in a saucepan. Cook and stir until mixture is very thick. Cool. Meanwhile cream margarine and sugar. Gradually beat in powdered sugar, until mixture is light and fluffy. Add the peppermint extract and food coloring. Finally, add flour mixture and beat until filling is creamy and smooth.
To prepare frosting:
Combine sugar and cream in a saucepan. Bring to a boil over medium heat, stirring constantly. Reduce heat and simmer 6 minutes. Remove from heat and stir in chocolate until melted. Next stir in the peppermint extract and butter. Chill until mixture thickens, then beat again until frosting is creamy and a good spreading consistency.
To assemble cake:
Place a bottom cake layer on platter and frost with 1/3 of the filling. Repeat twice. Top with remaining cake layer. Frost top and side of cake with frosting. Cut 8 Andes mints in half and arrange in a circle on the top of the cake. Shave 5 Andes mints into chocolate curls and place in the center of the circle to garnish.