Preheat oven to 350F.
In a large bowl, mix flour, baking powder, salt, baking soda and cinnamon. Set aside.
Remove the bowl from the ice water and scrape up the hardened butter. Transfer the butter to the bowl of a standing mixer beat until creamy.
Add sugars and cream, add eggs one at a time.
Gradually add flour mixture and mix well.
In another medium bowl, combine together the pumpkin puree and buttermilk.
Stir in the pumpkin mixture until well combined.
Pour the batter in a 13x9 baking pan lined with parchment paper.
Bake for 30-35 minutes. When done take it out leave it in the pan for 10 minutes, then transfer the cake to a cooling rack to cool completely.