Preheat oven to 350*. Grease and flour a 10- inch bundt pan. In a small non-reactive bowl, soak the raisins in the rum for at least 30 min or several hours. Meanwhile peel the sweet potatoes, cut them in half and then cut each half into 4-inch slices. Place the slices into a pot of cool salted water, cover and bring to a boil. Reduce to a gentle simmer and cook until the sweet potatoes are very tender. Drain off the water, allow the potatoes to air-dry for a few minutes, then use a pot masher or large fork to roughly mash them. Measure out 2 cups and set aside to cool.
In a large bowl with a whisk or the bowl of a stand mixer fitted with the paddle attachment beat the eggs a little just to break them up.
Add the sugar and beat until the mixture is thick and pale, about 2 minute Add the vegetable oil and vanilla, then beat to blend . Drain the raisins and set aside, but add ¼ cup of the rum macerating liquid to the batter. Add the sweet potatoes and mix thoroughly, scraping down the sides and bottom of the bowl.
Into a separate bowl, sift the flour, baking powder, baking soda, salt cinnamon and nutmeg. Add the flour mixture to the batter in 3 additions, alternating with the buttermilk in 2 additions, beginning and ending with the dry. Fold in the raisins.
Pour entire batter in pan.Bake1 hour to 1 hour and 20 min or until wooden skewer comes out clean and cake is just beginning to pull away from sides of pan. Cool the cake in the pan set on a wire rack for 10 min, then invert onto the rack. Set the rack over a baking sheet or large plate to catch the excess glaze. This cake must be glazed while still warm, so it absorbs the maximum syrup.
For the glaze, combine the brown sugar, butter, and cream in a small, heavy bottomed sauced pan. Bring to a boil over medium heat, stirring until the sugar dissolves. Continue to boil until the mixture thickens somewhat, about 3 minutes, stirring often. Remove the glaze form the heat and stir in the rum. With a long wooden or metal skewer poke holes all over the cake, concentrating on the top. Spoon about half the warm glaze over the cake and let the cake and remaining glaze cool for 10 to 15 minutes, until it has thickened slightly.
Pour the rest of the glaze over the cake, letting it dribble down the sides, then allow the cake to cool completely before cutting and serving or wrapping and storing.