HEAT oven to 350°F. Spray a 10-inch (12-cup) fluted tube pan with flour no-stick cooking spray.
COMBINE shortening, sugar, brown sugar, eggs, 1⁄3 cup sweetened condensed milk and vanilla. Beat at medium speed until creamy. Beat in buttermilk and cocoa until well blended.
COMBINE flour, baking soda, cinnamon and salt in medium bowl. Add to shortening mixture. Beat at low speed until blended. Beat at medium speed 5 minutes. Stir in hot water. Batter will be thin. Pour into prepared pan.
BAKE 40 to 50 minutes or until top springs back when touched lightly in center or until toothpick inserted into center comes out clean. Cool 20 minutes. Remove from pan. Place cake, fluted side up, on serving plate. Cool 10 minutes.
COMBINE powdered sugar, 1⁄2 cup sweetened condensed milk and 2 tablespoons shortening. Beat at high speed until glossy and of desired spreading consistency. Spread over warm cake. Sprinkle with nuts and marshmallows. Drizzle with chocolate syrup. Serve warm or cool completely