Instructions

• Preheat the oven to 325ºF (160ºC). Lightly butter a 9-inch (23 cm) springform pan and wrap the outside of the pan with aluminum foil to make it watertight. Set the wrapped springform pan inside a larger roasting pan or other pan that will hold a water bath.
• Place the chopped chocolate, 1/4 cup (60 ml) heavy cream, and 2/3 cup (160 ml) brewed espresso or strong coffee together in a large heatproof bowl.
• Set the bowl over a saucepan of simmering water (bain-marie), making sure the bowl does not touch the water. Stir gently until the chocolate is completely melted and the mixture is smooth. Remove the bowl from the heat and let it cool until it is warm but not hot to the touch (a few minutes).
• In a standing electric mixer fitted with the whisk attachment (or using a hand mixer), combine the 5 large eggs (room temperature), a pinch of salt, and 1/2 cup (100 g) sugar. Whip on high speed until the mixture is thick, pale, and holds soft peaks or ribbons when the whisk is lifted, about 5 minutes.
• Fold one-third of the whipped egg mixture into the warm chocolate mixture to lighten it, using a rubber spatula and gentle strokes to combine.
• Gently fold in the remaining whipped eggs in two additions, scraping the bowl sides and folding until no streaks remain. Do not overmix; keep the motion gentle to retain air.
• Scrape the batter into the prepared springform pan and smooth the top with a spatula.
• Pour warm (not boiling) water into the larger roasting pan until it reaches about halfway up the outside of the wrapped springform pan, creating the water bath.
• Carefully transfer the roasting pan with the springform pan into the preheated oven and bake for 50 minutes to 1 hour, until the cake is set at the edges but still slightly soft and jiggly in the center.
• When baking is complete, remove the roasting pan from the oven. Using oven mitts, lift the springform pan out of the water bath and place it on a cooling rack. Discard the water and unwrap the foil if desired.
• Let the cake cool completely to room temperature on the rack. To release, run a thin knife around the inside edge of the springform ring, then unlatch and remove the outer ring. Serve at room temperature or chill before serving, as desired.