- In a saucepan, bring the water and flax seeds to a boil. Reduce the heat and simmer for 30 minutes. Strain immediately, collecting the goopy liquid and separating it from the seeds. Let cool slightly, then refrigerate until lukewarm.
- With the rack in the middle position, preheat the oven to 180°C (350°F). Line the bottom of a 20-cm (8-inch) springform pan with parchment paper.
- In a bowl, combine the flour, baking powder and salt. Set aside.
- In another bowl, beat the sugar, cocoa powder, oil and vinegar with an electric mixer for about 3 minutes. Add the egg substitute and beat until smooth. Add the dry ingredients, alternating with the soy beverage and vanilla.
- Pour the batter into the cake pan. Bake until a toothpick inserted in the centre comes out clean, about 55 minutes.
- Let cool slightly. Unmould and let cool on a cake rack.
- Put the chocolate in a bowl. Set aside.
- In a saucepan, bring the soy beverage and corn syrup to a boil. Pour over the chocolate. Let sit for 1 minute while the chocolate melts.
- Whisk the chocolate mixture until smooth. Cover and refrigerate until the ganache is cold but still spreadable, about 1 hour. If necessary, soften by warming briefly in a microwave oven.
- Cut the cake horizontally in two. Ice the middle and outside with the ganache.
Pour the remaining egg substitute into ice-cube trays and freeze: 1 cube is equivalent to 1 egg.