This moist rum-raisin cake showcases the rich, butterscotch-y flavor of brown rice syrup. If you want extra sauce for drizzling atop each individual serving (who doesn't?), double the glaze.
To make the cake: Pour the rum over the raisins, cover, and set aside for at least 1 hour and as long as overnight.
Preheat the oven to 350°F.
In a large bowl, stir together the mashed sweet potato, eggs, brown rice syrup, sugar of your choice, oil, buttermilk (or yogurt), and vanilla until well blended. Drain the raisins and put 1/4 cup of the rum into the batter; reserve the rest for the glaze.
In a separate bowl, whisk together the flours, baking powder, baking soda, salt, and spices.
Add the dry ingredients to the wet and mix thoroughly, scraping the sides and bottom of the bowl. Add the drained raisins and mix to combine.
Grease and flour a 10-Cup Bundt pan (or 12 mini-Bundt wells, or silicone molds). Pour the batter into the prepared pan and bake for 50 to 55 minutes (30 to 35 for mini-cakes), until the top springs back when lightly touched and the edges just begin to pull away from the sides of the pan.
To make the glaze: Combine all of the ingredients in a small saucepan and bring to a boil. Remove from the heat.
Remove the cake from the oven and upend the pan onto a cooling rack. The cake should release easily; remove the pan and brush with the glaze immediately. Continue brushing until all of the glaze is used. Cool the cake for 1 hour before slicing.
Store any leftover cake, tightly wrapped in plastic, at room temperature for several days; freeze for longer storage.
