Heat oven to 350°F. Grease and flour two 9-inch round cake pans. In large bowl, combine cream cheese, 1/2 cup margarine, vanilla and peppermint extract; blend until smooth. Add powdered sugar alternately with hot water, beating until smooth. Add chocolate; blend well.
In another large bowl, combine 2 cups of the frosting mixture and 1/4 cup margarine; blend well. Beat in eggs 1 at a time, beating well after each addition. Lightly spoon flour into measuring cup; level off. Add flour, baking soda, salt and milk; beat until smooth. Pour batter evenly into greased and floured pans.
Bake at 350°F. for 30 to 40 minutes or until toothpick inserted in center comes out clean. Cool 5 minutes; remove from pans. Cool 1 hour or until completely cooled.
To assemble cake, place 1 layer, top side down, on serving plate. Spread with about 1/4 of frosting. Top with second layer, top side up. Spread sides and top of cake with remaining frosting. Store in refrigerator.