Grease a 1½-quart pudding mold thoroughly with butter and set aside.
In a large bowl, whisk together flour, baking soda, cinnamon, nutmeg, cloves, and salt.
In another bowl, combine molasses and hot water, stirring until well mixed.
Add the molasses mixture to the dry ingredients and stir until just combined.
Fold in raisins, currants, candied citron, and melted butter until evenly distributed.
Pour batter into the prepared pudding mold and cover tightly with the lid or aluminum foil.
Place mold on a rack in a large pot and add enough boiling water to come halfway up the sides of the mold.
Cover pot and steam for 3 hours, adding more boiling water as needed to maintain water level.
Remove from heat and let cool for 10 minutes before unmolding onto a serving plate.
Serve warm with hard sauce, whipped cream, or vanilla custard.