Spray a 9" Springform Pan with baking spray. Cut a 9" circle of parchment paper for the bottom. Place it in the greased pan, then spray the parchment paper lightly.
In a small saucepan, add the butter. Heat over medium heat until melted.
Add the brown sugar, and cinnamon. Stir until sugar has been melted and mixture is well combined. Add the Cream and stir until combined.
Pour mixture into the prepared cake pan, spreading to cover the bottom.
Slice the plums in half and twist to separate. Remove the pit. Slice each half into 1/8" -1/4" slices.
Arrange Plums in the Sugar/Butter base, working from the center outward, in a spiral pattern.