5 large eggs
9 ounces bittersweet chocolate, coarsely chopped
1 cup of sugar
5 tablespoons unsalted butter, cut into chunks
2 tablespoons coffee or water (I used water as no one in my house drinks coffee so I didn't have any)
1/3 cup all-purpose flour
Pinch of salt
For the Glaze (optional)
4 ounces bittersweet chocolate, coarsely chopped
½ cup heavy cream
2 teaspoons light corn syrup
Center a rack in the oven and preheat the oven to 350 degrees F. Butter a 9-inch springform pan, line the bottom with parchment paper, butter the paper, dust the inside of the pan with flour and tap out the excess. Place the pan on a baking sheet lined with parchment or a silicone mat.
Separate the eggs, putting the whites in a mixer bowl or other large bowl and the yolks in a small bowl.
Set a heatproof bowl over a saucepan of simmering water and add the chocolate, sugar butter and coffee. Stir occasionally until the chocolate and butter are melted; the sugar may still be grainy, and that's fine. Transfer the bowl to the counter and let the mixture sit for 3 minutes.
Using a rubber spatula, stir in the yolks one by one, then fold in the flour.
Here I am... about to over beat the egg whites...
Bake for 35 to 45 minutes, or until the cake has risen evenly (it might rise around the edges and you'll think it's done, but give it a few minutes more, and the center will puff too) and the top has firmed (it will probably be cracked) and doesn't shimmy when tapped; a thin knife inserted into the center should come out just slightly streaked with chocolate. Transfer the pan to a cooling rack and let the cake rest for 5 to 10 minutes.
Run a blunt knife gently around the edges of the cake and remove the sides of the pan. Carefully turn the cake over onto a rack and remove the pan bottom and the parchment paper. Invert the cake onto another rack and cool to room temperature right side up. As the cake cools, it may sink.
Cooling, and not terribly impressive...
To Make the Optional Glaze:
First, turn the cooled cake over onto another rack so you'll be glazing the flat bottom, and place the rack over a baking sheet lined with parchment or wax paper to catch any drips.
Put the chocolate in a small heatproof bowl.
Melt the chocolate over a pan of simmering water or in a microwave oven – the chocolate should be just melted and only warm, not hot. Meanwhile, bring the cream to a boil in a small sauce pan. Pour the hot cream over the chocolate and stir very gently with a rubber spatula until the mixture is smooth and shiny. Stir in the corn syrup.
Pour the glaze over the cake and smooth the top with a long metal icing spatula. Don't worry if the glaze drips unevenly down the sides of the cake – it will just add to its charms. Allow the glaze to set at room temperature or, if you're impatient, slip the cake into the refrigerator for about 20 minutes. If the glaze dulls in the fridge, just give it a little gentle heat from a hairdryer.