Preheat oven to 350 degrees F. and spray muffin tin generously with cooking spray or line 12 muffin cups with liners (foil liners recommended). If using paper liners, spray liners lightly with cooking spray before filling with batter.
In a large mixing bowl, add sour cream, oil, pumpkin, banana (chopping in bowl while stirring) and eggs. Stir until well combined. Slowly add flour, sugar, cinnamon, pumpkin pie spice, baking soda and salt, stirring until well combined. Fill muffin cups 1/2 full with batter.
Bake for 22-25 minutes, or until baked though. Remove and let cool.
To prepare icing, place powdered sugar into a medium mixing bowl and add whisk in heavy cream until nice drizzling consistency. Drizzle evenly over each muffin cup. Serve room temperature or chilled.