Directions for Cake
Combine the raisins and spiced rum and soak overnight, covered and at room temperature.
Preheat the oven to 250°F. Coat a 10-inch tube pan with Pan Grease (page 16) or a thin layer of butter with a light dusting of flour.
Drain the raisins. (Save the rum for the buttered rum sauce.) Pat the raisins dry and toss them with ¼ cup of the all-purpose flour in a colander.
In a medium bowl, sift together the remaining 3 cups flour, the baking powder, and salt.
In the bowl of a stand mixer fitted with the whisk attachment, beat together the butter, shortening, and sugar on high speed until fluffy, 3 minutes. Reduce the speed to low and beat in the eggs. Scrape down the sides and around the bottom of the bowl. Beat on high speed for 2 minutes. Add the flour mixture along with the milk and vanilla. Beat on low speed to combine. Scrape down the sides and around the bottom of the bowl. Beat on high speed for 1 minute. Using a rubber spatula, carefully fold in the raisins. Pour the batter into the prepared pan and smooth the top.
Bake the cake until it is golden brown and begins to pull away from the sides of the pan, about 2½ hours. During baking, do not open the door or the cake will fall. Remove the cake from the oven and cool in the pan for 20 minutes before turning it out onto a wire rack to cool completely.
After placing the cake on a serving plate, poke holes in the cake with a skewer and pour the warm rum sauce over the top. You can also serve the cake by the slice and drizzle the warm rum sauce over a piece at a time.
hint Soak the raisins in rum at least one day ahead of making the cake for the most flavorful, rum-infused taste. You can serve the cake right away, but I recommend covering the cake and letting it sit at room temperature for a day or two.
Directions for Pan Grease
In the bowl of a stand mixer fitted with the whisk attachment, beat the shortening, oil, and flour on low speed until incorporated. Scrape down the sides and around the bottom of the bowl and continue beating on high speed until velvety smooth without any lumps, 3 minutes. The coating will keep in the fridge in an airtight container for up to 3 months. Whisk thoroughly before each use.
Directions for Hot Buttered Rum
In a 1-quart saucepan set over medium-high heat, melt the butter. Add the brown sugar and cook, stirring constantly, until dissolved, 5 minutes. Remove the pan from the heat and whisk in the rum. If you want the alcohol to evaporate, cook over medium-high heat, stirring constantly, for 5 minutes, or to thicken, reduce the heat and cook for an additional 5 minutes. The sauce will keep in an airtight container in the refrigerator up to 2 weeks. It is best to reheat it before serving.