Preheat oven to 350 degrees F. Grease a 10-inch or 9-inch loaf pan with butter and set aside.
In a medium bowl mix together flour, baking powder, salt, pumpkin spice and set aside.
In the bowl of an electric mixer, fitted with the wire whisk attachment, cream together butter, cream cheese and sugar on medium speed until fluffy. Add the eggs one a time, beating well after each addition. With the motor running on low, add the flour mixture followed by the pumpkin puree. Mix on low until combined.
Pour the batter into the prepared pan and bake for 1 hour to 1 hour and 15 minutes. Check for doneness by inserting a toothpick into the cake, it should come out clean.
Once baked, cool the pound cake in the pan for 30 minutes before transferring onto a wire rack to cool completely.
White Chocolate Whipped Ganache:
In a medium bowl set over a medium saucepan of simmering water, melt the white chocolate. Remove from the heat and set aside. Discard the water from the sauce pan, add the heavy cream and butter to the saucepan and heat until the butter is melted and small bubbles appear around the edges.
Whisk the hot cream mixture into the white chocolate. Lumps will start to appear, don't be afraid, continue to quickly mix until the mixtures combine and the lumps disappear. Set the bowl in a cool place for at least 1 hour.
Once the ganache has cooled down, using a hand mixer or an electric mixer whisk in the powdered sugar. Once you did this, cool the mixture for a few minutes only and cover the cake with it.
Keep ganache leftovers in the fridge. The ganache can be kept in an airtight container for up to two weeks. Before using, place in on the counter for two hours, since it will harden in the fridge