1. Preheat oven to 350 degrees Fahrenheit.
2. Mix flour, sugar, cocoa, baking soda, baking powder, vanilla sugar, and salt. Add eggs, orange juice, and oil, and mix until smooth. Add boiling water (once batter is well mixed, so eggs do not cook) and mix. Pour batter into a well-greased Bundt pan. Bake for 45 minutes. Let cool fully.
3. To make the filling, beat margarine and marshmallow fluff until light and fluffy. Add confectioners’ sugar and soy milk and mix until incorporated.
4. To make the glaze, combine confectioners’ sugar, cocoa, hot water, and oil. Whisk until smooth.
5. When the cake has fully cooled, flip onto a platter, then carefully cut the cake in half horizontally. Remove the top half of the cake and set aside. Use a spoon to scoop some holes out of the inside of the cake without making any holes through the bottom of the cake, and fill with marshmallow filling. Carefully place the top of the cake back on and drizzle with chocolate glaze.