Combine first 8 listed ingredients in a bowl. In another, combine maple syrup, baking soda mixture and melted butter, and then quickly whisk in eggs. Mix wet mixture into dry until well-combined. Spoon into a buttered or vegetable-sprayed 6-cup pudding mould (available at kitchenware stores).
Cover tightly - with lightly buttered foil if mould does not have a lid - and place in a roasting pan. Pour water into the pan to a depth of 2 inches. Cover pan and bake pudding in 325 degree F oven 1 1/2 hours, or until pudding is puffed and springs back when gently touched. When cooked, uncover and cool for 10 minutes. Unmould pudding onto a serving plate. Serve with hard sauce, sweetened whip cream or ice cream.
Note: Pudding can be cooked several days ahead, cooled, wrapped tightly, and stored in the fridge. Reheat for about 5-8 minutes in the microwave before serving. Yams are the orange-fleshed variety of sweet potato. 1 small to medium size yam will yield the required amount.