1. Prepare a 9 inch springform pan with non-stick spray.
2. In a large saucepan, melt the butter and marshmallows over medium-low heat. Heat and stir until completely melted.
3. Add the cinnamon toast crunch and stir until well coated.
4. Pour the mixture into the prepared pan and use a spatula sprayed with non stick spray to help press the cereal into the pan in an even layer.
5. Refrigerate the cereal treat until completely cooled.
6. For the remaining layers, you can resume the same pan once the previous layer is cooled, or you can use additional springform pans. Whichever you choose, prepare the springform pan again with non-stick spray.
7. Repeat step 2, then add the chopped cinnamon rolls and gently stir until well coated.
8. Pour the mixture into the prepared pan and use a spatula sprayed with non stick spray to help press the cereal into the pan in an even layer.
9. Refrigerate the cinnamon roll treat until completely cooled.
10. Repeat the treat making process with the chopped donuts, gently stirring the mixture together and pressing into the pan.
11. Once all three layers are made and cooled, place the cereal layer on a cake stand or other serving plate.
12. Spread about 1/2 cup of marshmallow cream, or just enough to have a light coat on top of the treat layer, into an even layer on top.
13. Add the cinnamon roll treat layer, then repeat adding another 1/2 cup marshmallow cream.
14. Top the cake with the donut layer.
15. To make the icing, combine all ingredients except for the powdered sugar in a small sauce pan. Heat on low until sugar is melted, then turn heat to medium to bring to a boil. Boil for 3 minutes, stirring occasionally, then remove from heat and immediately pour into a heat-proof glass bowl.
16. Whisk in powdered sugar and allow to cool slightly and thicken. If you find your icing to be a little thick, just add a touch more water to thin it back out.
17. Drizzle the icing down the sides of the cake while still a little warm. It will be too firm to pour and get a nice drizzle if it cools completely.
18. Spread the remaining icing over the top of the cake.
19. To make the frosting, beat the butter and shortening together until smooth.
20. Slowly add half of the powdered sugar and mix until smooth.
21. Add the vanilla extract and water or milk and mix until smooth.
22. Slowly add remaining powdered sugar and mix until smooth.
23. Pipe swirls of frosting around the top of the cake. I used Ateco tip 808. Finish of the cake with additional donuts.
24. Store cake in an airtight container in the fridge until ready to serve. Cake is best for 2-3 days.