For the chocolate mousse cake, preheat the oven to 175-180ºC top/bottom heat. Grease a springform pan with margarine and crumble it.
Mix flour, cocoa powder, sugar, baking soda and salt. Measure oil, vegetable milk, vanilla extract and lemon juice in a measuring cup and add to dry ingredients. Mix quickly with a whisk.
Pour batter into pan and bake for 30 to 40 minutes. For the chocolate mousse, gently melt the chocolate, whip silken tofu with vanilla sugar, rum and chocolate with a hand mixer until fluffy. Cut the cooled chocolate cake in half.
Spread about a third of the chocolate mousse on the cake base, place the other part on top and cover the cake with the remaining chocolate mousse.
Decorate the chocolate mousse cake with the chocolate flakes and let it set overnight in the icebox.