- Preheat the oven to 180 °C (350 °F).
- Line two 23-cm (9-inch) round pans with parchment paper, butter and flour. In a bowl, sift together the flour, cocoa powder and baking powder. Set aside.
- In another bowl, with an electric mixer on high speed, beat the eggs, cream of tartar and sugar until the mixture doubles in volume, about 8 minutes. Add the oil, buttermilk and vanilla. Reduce the speed of the mixer. Add the dry ingredients, combining quickly.
- Pour into the pans. Bake in the middle of the oven for about 45 minutes or until a toothpick inserted in the centre of the cake comes out clean. Cool completely on a rack. Cut each cake in half horizontally.
- In a saucepan, bring the sugar and water to a boil.
- In a bowl, beat all the ingredients until the mixture becomes light and fluffy.
- Brush syrup on each cake layer. Layer with frosting. Finish by frosting the cake evenly.