Preheat the oven to 325°F.
Spray 8.5" by 4.5" loaf pan with nonstick cooking spray. Line the bottom and long sides with a single piece of parchment. Cut the piece slightly too tall so it peaks over the sides of the pan.
In a medium bowl, combine flour, baking soda, salt, and all spices. Set aside.
In a small bowl, whisk together molasses and sour cream. Set aside.
Beat together butter and brown sugar in mixer until light and fluffy.
Add eggs one at a time, beating well between each addition and scraping down the sides of the bowl as needed.
Althernate adding portions of the dry mixture and molasses mixture, starting and ending with the dries. Mix until just smooth. Scrap bowl between additions.
Pour batter into pan and smooth top. Bake for 1 hour 10 minutes.
Set the pan on a wire rack to cool. Remove cake from pan once it is cool enough to be handled.
To Serve: Dust slices with powdered sugar and top with whipped cream.