In a blender or food processor, whirl persimmon pulp and baking soda until smooth.
In a bowl, with a mixer on medium speed, beat sugar, 1/2 cup butter, and molasses until blended. Add eggs and vanilla and beat until smooth. In another bowl, mix flour, cornmeal, cinnamon, ginger, and allspice. Stir dry ingredients and persimmon purée into sugar-butter mixture. Add raisins and walnuts and mix until blended.
Pour batter into a buttered and floured 7- to 8-cup loaf pan or ring mold (no deeper than 3 in.); cover tightly with foil. Put pan in a larger pan and place in a 300° oven. Add 3/4 inch boiling water to outer pan around loaf pan or 1/2 inch boiling water around ring mold.
Bake until pudding is firm in center when lightly pressed (lift foil to check), about 2 hours (about 1 1/4 hours in a convection oven). Carefully lift pan from water and let stand 10 minutes, then uncover. Run a knife between pudding and sides of pan to release. Invert onto a plate. Cut warm or cool pudding into slices, transfer to plates, and top with spoonfuls of persimmon-eggnog sauce.