To prepare pudding, butter a 6-cup soufflé dish. Set aside a large pot with a lid that will hold a water bath.
2. Place cranberries in a medium saucepan. Cover with water. Cover and cook over medium heat until cranberries begin to burst and water is absorbed, about 15 minutes.
3. Beat together egg, sugar and molasses. Combine baking soda and 1/3 cup hot water; stir well. Add to egg mixture. Combine salt and flour; add to egg mixture. Do not overmix. Stir in cranberries.
4. Pour batter into prepared soufflé dish. Cover with foil. Place dish in the large pot. Add several inches of water. Cover pot and bring water to a boil. Reduce heat, cover and simmer 70 to 90 minutes, until firm. Unmold onto a serving platter.
5. To prepare sauce, combine all ingredients in a saucepan. Cook over low heat until thickened, about 30 minutes, stirring occasionally. Place warm sauce in a bowl or pitcher to pass with the pudding.