In a medium bowl, whisk together the brown sugar, molasses, milk, oil, sour cream, egg, and vanilla extract until well blended. In a large bowl, whisk or sift together the flour, baking powder, baking soda, salt, ginger, cinnamon, allspice, cloves, and nutmeg. Add the wet ingredients to the dry ingredients, stirring just until combined. The batter will still be slightly lumpy, which is fine – do not overmix.