Heat oven to 350°F. Spray a 10-inch (12-cup) Bundt pan with no-stick cooking spray with flour; set aside.
2. Measure 1/3 cup sweetened condensed milk for cake. Reserve remaining milk for frosting.
1. Combine shortening, granulated sugar, brown sugar, eggs, 1/3 cup condensed milk and vanilla extract; beat at medium speed until creamy. Add buttermilk and cocoa; beat until well blended.
2. In a medium bowl, combine flour, baking soda, cinnamon and salt. 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.
3. Bake 40 to 50 minutes or until top springs back when touched lightly in center or until toothpick inserted into center comes out clean.
4. Cool 20 minutes before removing from pan. Place cake, fluted side up, on serving plate. Cool 10 minutes.
1. In the bowl of an electric mixer combine powdered sugar, 1/2 cup reserved sweetened condensed milk and 2 tablespoons shortening; beat at high speed until glossy and of desired spreading consistency.
2. Spread over warm cake. Sprinkle with nuts and marshmallows.
3. Drizzle with chocolate syrup. Serve warm or cool completely.