Line the cake tin with baking paper. Roughly chop the raisins and flavour with the rum. Roast the walnuts in a oven toaster for 5 minutes and roughly chop.
Pulverize the oatmeal in a food processor. Fill the steamer with water and set over heat.
Put the soy milk, sugar, salt, raisins, walnuts, and oatmeal in a bowl and mix well to allow the oatmeal to absorb the liquid ingredients.
Sift in the ingredients marked with ★ and, using a rubber spatula, fold the mixture together until it's no longer powdery and has an even texture.
Pour the mixture into the cake tin. Make a slight dent in the center of the mixture using a spatula.
Once the steam starts rising from the steamer, place the cake tin inside and steam on high heat for 30 minutes. Test to see if the cake is done by inserting a skewer into the center. If it comes out clean, it's ready. This completes the fluffy sponge.
Once cooked, remove the sponge from the tin and leave to cool. Slice away any parts of the top of the cake which have expanded too much (you can use these slices for taste testing ♪), then slice the cake into 2 layers. I recommend using a wet knife for easy cutting.
Once the sponge has completely cooled, decorate with the dairy-free chocolate cream.
To decorate: Spread the chocolate cream over the top of one layer of sponge, then sandwich the other layer on top of that.
Spread cream over the top of the cake and even it out with a spatula. Lift the cream, a dollop at a time, over the sides of the cake, then evenly spread it all the way around.
Use the leftover cream to fill in any gaps and smooth everything out with a fork or spatula. Decorate with walnuts to finish.
When cutting to cake, it's easiest to use a wet knife. Clean the knife after each cut to get a nice, neatly sliced cake.
Story Behind this Recipe
This is a variation of the recipes for "Oil- & Egg-Free Steamed Shortcake" (Recipe ID: 771211) and "Steamed Oatmeal, Walnut & Cocoa Bread" (Recipe ID: 754842).
This is a rich chocolate sponge cake with a moist and chewy center. It doesn't keep well, so I suggest eating it all within a day and storing it in the refrigerator. Cover the lid of the steamer with a cloth and secure in place with a rubber band to prevent the lid from dripping when removed.