Dissolve the baking soda in the hot water. Stir in 1 tablespoon of sugar and molasses, then mix in the cranberries and flour. Pour into a greased 6 cup steamer mold.
Cover the mold, and place into a steamer basket over boiling water. Cover the steaming pot. Cook over medium heat for one hour before checking, but it will take about 1 1/2 hours total. A toothpick inserted into the pudding should come out clean. Loosen the edges, and cool on a wire rack in the mold.
Make the hard sauce just before serving: Heat the unsalted butter, cream, 1 cup sugar and vanilla in a small saucepan over medium heat. Cook stirring constantly until heated through and smooth.