Step 1

Preheat oven to 325°F / 165°C. Lightly grease a 9 or 10" / 23-25 cm round springform pan. Optionally, line bottom of pan with a circle of parchment paper. Get out a pan, such as a roasting pan, large enough to hold the cake pan (for a water bath). Set up a medium pot with water to use as a double boiler.

Step 2

Finely chop both types of chocolate. Brew the coffee.

Step 3

In a double boiler over simmering water, melt the bittersweet and unsweetened chocolates with coffee, while stirring. Set aside.

Step 4

In a stand mixer fitted with the whisk attachment, whisk together the eggs and sugar. Remove the bowl from the mixer and set the bowl over simmering water. Whisk continually over steam for 2 minutes, until the mixture is warmed and the sugar is dissolved. (To test if the sugar has dissolved, rub a bit of the mixture between you thumb and index finger; it should be smooth, not gritty.)

Step 5

Re-attach the bowl to the mixer and beat at medium speed until lightened with significantly increased volume, 3-4 minutes. Reduce speed to medium-low and continue beating for 2 minutes. Set aside.

Step 6

Beat the cold cream until it's right between the stage where it holds soft peaks and firm peaks. It should dollop nicely, neither spreading nor holding its shape.

Step 7

Whisk the egg mixture. Fold about a quarter of the egg mixture into the chocolate mixture. Fold this lightened chocolate mixture into remaining egg mixture. (It will require a lot of folding.)

Step 8

Next, fold in the whipped cream gently until fully combined.

Step 9

Transfer the batter to the prepared pan, smoothing the top.

Step 10

Place the filled cake pan inside the larger baking or roasting pan. Pour water into the outer pan to come about halfway up the sides of the cake pan. Insert into the heated oven.

Step 11

Bake 30 minutes. Open oven door 30 seconds to release any moisture that may have developed in the oven.

Step 12

Continue baking until center of cake feels somewhat firm when lightly pressed, 25-30 minutes.

Step 13

Let cake cool in the turned-off oven 2 hours.