Heat oven to 350°F. Butter and flour a 10–12 cup Bundt pan.
Whisk flour, baking soda, baking powder, salt, ginger, cinnamon, cloves, nutmeg, allspice, and orange zest.
Beat softened butter with brown sugar and granulated sugar until light and fluffy.
Add eggs one at a time, beating briefly after each addition.
Mix in molasses and vanilla until fully combined and glossy.
Stir in dry ingredients in two additions, alternating with buttermilk. Begin and end with dry.
Blend in the hot water just until the batter is smooth and pourable.
Scrape batter into the pan, smooth the top, and tap to release bubbles.
Bake 45–55 minutes, until a tester comes out clean from the center.
Cool 15 minutes on a rack. Invert, then cool completely before glazing.
Whisk confectioners’ sugar, milk, and vanilla until thick but pourable.
Drizzle glaze over the cooled cake. Let set 15 minutes before slicing.