Adjust oven rack to middle position and preheat oven to 350°F. Spray 9-inch springform pan with baking spray. Press a square piece of parchment into bottom and up sides of pan and coat with baking spray. Press second piece of parchment into pan; coat with baking spray.
In medium bowl, whisk together flour, baking soda, salt, cinnamon, cloves, and allspice. In 2-cup liquid measuring cup or small bowl, whisk together molasses and boiling water until thoroughly combined.
In large bowl, beat together butter and brown sugar with an electric mixer on medium speed until light and fluffy, about 3 minutes. Add eggs, one at a time, beating well after each addition and scraping down sides and bottom of bowl with rubber spatula as needed. Beat in pumpkin puree and ginger. Reduce speed to low, then add flour mixture in 3 batches, alternating with molasses mixture.
Scrape batter into prepared pan and bake until cake tester inserted in center of cake comes out clean, about 45 minutes.
Cool cake in pan 10 minutes. Release springform and transfer cake directly onto cooling rack. Cool completely, at least 1 hour. Dust with confectioners’ sugar and serve.