With the rack in the middle position, preheat the oven to 350°F (180°C). Butter a 6-inch (15 cm) springform pan with removable bottom. Line the bottom of the pan with parchment paper.
In a bowl, combine the flour, cocoa powder, baking soda and baking powder.
In another bowl, whisk together the egg, sugar, oil and vanilla. Add the dry ingredients alternating with the buttermilk. Mix until smooth. Pour into the prepared pan.
Bake for 35 minutes or until a toothpick inserted in the centre of the cake comes out clean. Let cool on a wire rack before unmoulding.
Passion Fruit Cream
Butter a 6-inch (15 cm) springform pan with removable bottom. Line the bottom of the pan with parchment paper.
Extract the juice from the passion fruits into a sieve set over a bowl. You will need 4 tsp (20 ml) of juice.
Sprinkle the gelatin over the passion fruit juice and let bloom for 5 minutes.
To make the cream, whisk together the egg yolks and sugar in a pot off the heat until smooth.
Gradually whisk in the warm milk. Cook over medium-low heat for 5 minutes, stirring constantly with a wooden spoon, or until the cream thickens and coats the back of the spoon. Remove the pot from the heat.
Whisk the gelatin mixture into the hot cream until dissolved. Pour the cream into the prepared pan. Let cool. Cover and refrigerate for 1 hour or until the cream has set and chilled completely.
Place the chocolate in a bowl. Set aside.
In a pot, or in a microwave oven, bring the cream to a boil. Remove from the heat and pour over the chocolate. Let sit for 1 minute without stirring.
Whisk until the ganache is smooth. Stir in the butter and passion fruit syrup. Cover and refrigerate for 30 minutes or until the ganache is spreadable.
Cut off the rounded top of the cake. Cut the cake in half horizontally to get a total of 2 cake layers. With a pastry brush, cover both layers of cake with the passion fruit syrup.
Pass a thin blade between the passion fruit cream and the side of the pan. Unmould. Turn the passion fruit cream over onto one of the cake layers. Remove the parchment paper and top with the remaining cake layer.
Cover the entire cake with the ganache. Decorate the top of the cake with white chocolate hearts, if desired. To make these decorations, first melt the white chocolate. Transfer the melted chocolate to a small parchment paper cone (see note). Cut the tip off the cone and drizzle the white chocolate over the cake, forming hearts or other decorations of your choice.
Passion fruits are available in some grocery stores and in most fruit stores all year round.
Passion fruit syrup is available in some grocery stores or specialty shops usually in the wine aisle.
Recipes with the "Healthy Pick" stamp have been evaluated by a registered dietitian member of the Ordre professionnel des diététistes du Québec.