Oven 350 deg F
Coat a 9 inch springform pan with cooking spray
Toss raisins and rum in a small bowl ans let stand. Whisk flour, nutmeg, and salt in another bowl.
Mash sweet potato in a large bowl (you should have about 1-3/4 cups). Add eggs;beat with an electric mixer on medium until combined. Add coconut milk, 1 cup brown sugar and butter; beat until combined. Stir in the dry ingredients until evenly moistened. Stir in the raisins and any remaining rum. Spread the batter in the prepared pan.
Topping;
Combine topping ingredients and sprinkle on top of cake.
Bake the cake until a knife inserted into the center comes out clean, 1 to 1-1/4 hours. Let cool in the pan for 10 minutes. Run a knife around the edge of the pan and remove the side ring. Let cool at room temp for 1 hour, then refrigerate until cold, about 3 hours.