Preheat the oven to 325 degrees F. In a large bowl, mix together flour, baking powder, and salt. In a separate bowl, use an electric mixer fitted with a paddle to beat the butter and cream cheese together until smooth and creamy. Add the sugar to the butter and cream cheese and beat until light and fluffy. Add the vanilla and beat for another minute. Add each egg, one at a time, and beat for a minute in between each addition. Add the pumpkin pureé and beat until well combined and smooth. Add the entire flour mixture and beat on low until combined. Grease and flour a 9 x 5 loaf pan and pour batter into the pan. Using a rubber spatula, spread the batter into the corners in an even layer. Bake the cake for 60-75 minutes until a toothpick inserted into the middle comes out clean. Check the cake at 30 minutes to make sure it's not getting too brown and rotate the pan. If the cake is browning too much, move to an upper rack to finish baking.