- With the rack in the middle position, preheat the oven to 350°F (180°C). Butter two 8-inch (20 cm) springform pans and line the bottoms with parchment paper.
- In a bowl, combine the flour, brown sugar, cocoa powder, baking powder, baking soda and salt. Set aside.
- In another bowl, combine the chocolate and oil with an electric mixer. Add the eggs and beat until smooth. At low speed, add the dry ingredients alternately with the milk. Gradually add the boiling water and combine until smooth. Spoon the batter into the prepared pans.
- Bake for 35 minutes or until a toothpick inserted into the centre of the cake comes out clean. Let cool completely. Unmould.
- Adjust the oven temperature to 200°F (100°C). Line a baking sheet with parchment paper. On the underside of the parchment paper, draw two 8-inch (20 cm) circles using a pencil.
- In a bowl placed over a pot of simmering water, heat the sugar and egg whites, whisking constantly, until the sugar dissolves. Remove from the heat. Beat the mixture with an electric mixer until stiff peaks form.
- Spoon the meringue into a pastry bag fitted with a 1/2-inch (1 cm) plain round tip. Pipe the meringue into a disc inside each circle, 1/2 inch (1 cm) from the line. With a spatula, gently smooth the surface, if needed.
- Bake for 2 hours or until the meringues are dry and easily peel off the paper. Turn off the oven and let them dry for about 2 hours or overnight, leaving the oven door slightly ajar using a wooden spoon.
- Place the egg whites in a bowl.
- In a small saucepan, bring the sugar, water and corn syrup to a boil until a candy thermometer reads 235°F (113°C). Remove from the heat.
- Beat the egg whites with an electric mixer on medium speed until frothy. Drizzle the hot syrup onto the egg whites, avoiding the mixer’s beaters. Increase the speed and beat continuously until cooled and stiff peaks form, about 30 minutes (see note).
- Cut and discard the rounded tops of each cake.
- On a cake stand or serving plate, place 1 slice of cake. Spread with 1 cup of the Italian meringue and cover with a meringue disc. Spread with 1 cup of Italian meringue and cover with a second slice of cake. Spread with 1 cup of Italian meringue and cover with the second meringue disc. Ice the entire cake with the remaining Italian meringue.
The meringue discs and cake can be made a day in advance, wrapped and kept at room temperature. However, the Italian meringue must be made just before assembling; otherwise it will set and no longer be spreadable.