In medium saucepan, place peeled chunks of sweet potato. Add a pinch of salt and bring to a boil. Turn down to simmer and cook until tender, about 15 minutes. Drain and mash to a smooth puree. Measure out 1 1/2 cups puree.
In medium bowl, combine sweet potato puree, butter, brown sugar, and canela. Mix well. In glass measure, combine milk and eggs. Beat with a fork until combined. Add rum to this mixture.
Add milk mixture to sweet potato mixture and mix well. Add flour and baking powder and mix to combine thoroughly.
Grease a pyrex mold (loaf pan or round) with butter. Pour batter into pan. Bake in a pre-heated 350°F oven for about 25 minutes, or until a tester inserted into center of pudding comes out clean. Serve warm or at room temperature with a dollop of whipped cream.