Dissolve the baking soda in hot water.
Add sugar and molasses, mixing well.
Mix in cranberries and flour.
Pour into a greased 6-cup steamer mold.
Place mold in steamer, cover pot.
Cook over medium heat for 1 1/2 hours or until a toothpick inserted into center comes out clean.
Loosen the edges, and cool on a wire rack in the mold.
Serve with hard sauce.
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.