In a small saucepan, bring the water and flaxseed to a boil. Simmer over low heat for 30 minutes. Drain the mixture, keeping only the viscous liquid coming from the seeds. Let cool.
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, whisk together the sugar, cocoa powder, oil and vinegar with an electric mixer for about 3 minutes. Add the egg substitute and beat until well blended. Add the dry ingredients alternately with the soy beverage and vanilla.
Pour the batter into the pan. Bake for 55 minutes or until a toothpick inserted in the centre of the cake comes out clean.
Let cool before unmoulding and let completely cool on a wire rack.
Place the chocolate in a bowl. Set aside.
In a small saucepan, bring the soy beverage and corn syrup to a boil.
Pour over the chocolate and let melt for 1 minute. Whisk until the ganache is smooth. Refrigerate for about 1 hour or until the ganache has thickened and is spreadable. If needed, soften quickly in the microwave oven.
Cut the cake in half horizontally. Fill and frost the cake with the ganache.
Freeze the remaining egg substitute in an ice cube tray. 1 cube averages 1 egg.
Recipes with the "Healthy Pick" stamp have been evaluated by a registered dietitian member of the Ordre professionnel des diététistes du Québec.