Preheat oven to 325°F. Spray a standard loaf pan and line with parchment paper. In a medium bowl, whisk together flour, baking soda, salt, gingerbread spices; set aside. In a small bowl, whisk together molasses and sour cream; set aside.

Using an electric mixer on medium speed, beat together butter and brown sugar until light and fluffy, about 3 minutes. Add eggs one at a time, beating well between each addition and scraping down sides of the bowl as needed. Reduce mixer speed to low and add flour mixture in three additions alternately with the molasses mixture, starting and ending with the flour. Mix just until smooth. Give the batter a final stir with a rubber spatula to ensure all of the ingredients are incorporated.

Scrape batter into prepared loaf pan and smooth into an even layer. Bake until a thin knife inserted into center comes out clean, 1 hour 20 minutes to 1 hour 30 minutes. Allow cake to cool completely in pan set on a wire rack. Remove cake using the parchment paper, dust with powdered sugar and serve with fresh whipped cream. Leftover cake should be wrapped tightly in plastic wrap and kept at room temperature for up to 5 days (or frozen up to 2 months).