Preheat oven to 350°F. Grease an 8 ½ x 4 ½ inch loaf pan; set aside.
In a medium bowl, whisk together flour, baking powder, baking soda, cinnamon, ginger, nutmeg, cloves, allspice, and salt. Set aside.
In another medium bowl, whisk together the milk, molasses, egg, and vanilla extract. Set aside.
In a large mixing bowl, use an electric mixer on medium-high speed to cream together the butter and brown sugar until light and fluffy, about 2-3 minutes.
With the mixer on low, alternately add the flour mixture and the molasses mixture, starting and ending with the flour mixture. (i.e., add ⅓ of the flour mixture, then half of the molasses mixture, another ⅓ of the flour mixture, the remaining ½ of the molasses mixture, and finally the remaining ⅓ of the flour mixture). Mix just until combined; do not over-mix.
Add the sour cream; mix just until combined.
Transfer the batter to the prepared loaf pan. Bake for 45-55 minutes, or until a toothpick inserted in the center comes out clean.
Transfer to a wire rack to cool completely.