Preheat the oven to 350°F (180°C). Lightly grease three 8-inch (20 cm) cake pans. Line the bottoms with parchment paper and dust the sides with flour, tapping out any excess.

Melt the chocolate. Pour the hot coffee over the chocolate in a small bowl. Let sit for 1 minute and then whisk until the mixture is smooth.

Mix the dry ingredients and cut in the butter. Sift the flour, granulated sugar, cocoa powder, baking soda, baking powder and salt into a large mixing bowl or the bowl of a stand mixer fitted with the paddle attachment. Stir in the brown sugar. Add the diced butter and oil, working them in using electric beaters or the mixer on medium speed, until large pieces of butter are no longer visible, about 3 minutes.

Add the liquid, eggs and chocolate. Whisk the milk, eggs, egg yolks and vanilla together and add all at once to the flour mixture. Mix on low speed until combined, then increase the speed to medium and beat until smooth and thick, about a minute. Add the melted chocolate and mix again on medium speed until smooth, about 2 minutes. Divide the batter evenly between the pans and spread to level them, giving the pans a tap to knock out any air bubbles.

Bake the cakes for 30 to 35 minutes, until a tester inserted in the centre of a cake comes out clean. Cool the cakes in their pans on a rack for 15 minutes, then turn them out onto the rack to cool completely.

Make the creamy truffle filling. Place the chocolate and butter in a large bowl and set aside. In a medium saucepan, whisk the sugar, cocoa powder and cornstarch together. Whisk in the water, milk and egg yolks. Bring to a simmer over medium heat, whisking constantly, until the mixture thickens, turns glossy and a few bubbles just begin to break the surface, about 6 minutes. Scrape the filling into the bowl of butter and chocolate, whisking until both are melted. Stir in the vanilla. Place a piece of plastic wrap or parchment paper on the surface of the filling, cool for 1 hour on the counter and then chill for at least 4 hours before using.

Make the ganache topping. Place the chopped chocolate in a mixing bowl. Heat the cream and butter over medium heat until it comes to a simmer, pour it over the chocolate and let sit for a minute. Slowly whisk or stir the ganache until it is smooth. Let cool for 30 minutes and then chill for another 30 minutes until spreadable.

Assemble the cake. Place a cake layer on a cake stand or cake wheel. Spread a generous quarter of the creamy filling evenly over the cake and top with a second cake layer. Spread another quarter of the filling over the cake and then top with the third cake layer. Spread most of the remaining filling over the top, making it as level as possible. Spread any remaining filling around the sides of the cake. If the ganache is still too fluid to set, chill the cake until ready.

Spread the ganache over the top of the cake, coaxing it down from the top edge and around the sides of the cake. Chill, uncovered, until ready to serve.