Le Marquis chocolate sponge cake with chocolate butter icing

Put the semi-sweet baking chocolate and the strong coffee in a small saucepan.

Set the small saucepan inside a bigger pan of simmering water and leave it until the chocolate is completely melted.

Beat the egg yolks, gradually adding the sugar, until pale yellow and thickened -- the ribbon stage, where the mixture falls off the beaters and sits on the surface a second before disappearing.

Beat the butter into the melted chocolate and return it to the simmering water briefly to melt the butter in, until smooth and glossy.

Whip the egg whites with a pinch of salt from low up to high.

At the foamy stage add the cream of tartar and continue to stiff peaks.

Transfer the yolk mixture to a fresh bowl so the crusted sides do not go into the batter.

Fold the tepid chocolate and butter into the yolk mixture, then fold in a quarter of the whites, rotating counterclockwise, then more in stages.

If the whites have been over-beaten, fold in an extra egg white to loosen them.

Fold in the cake flour very gently; it is meant to be alternated with the whites.

Divide the batter evenly between two greased, parchment lined cake pans.

Bake at 350F; the book says around 25 minutes. He checked at 13 minutes, the toothpick came out clean and he pulled them, which was wrong.

Let the cakes stand 10 minutes, and once they start to sink run a knife around the edge and turn them out onto a cooling rack for two hours.

For the icing, melt the semi-sweet baking chocolate with the strong coffee in a small saucepan set in the simmering water.

Stir the butter into the melted chocolate and coffee until smooth and glossy.

Set the bowl over ice water and keep stirring until it reaches a spreading consistency.

Rescue for an underbaked cake: cover with foil and return to a 300F oven, slow cooking until cooked all the way through -- about another 10 minutes.

Ice the bottom layer, set the second layer on top and cover the outside with icing.

For a second batch of icing, melt the chocolate with four tablespoons of rum, stir in butter a tablespoon at a time up to 10 tablespoons, then stir over ice water to a spreading consistency.

Stop stirring short of the full set so the icing stays shiny and glossy, and spread it over the cake.