Preheat the oven to 190ºC / 375ºF conventional oven. Grease a 23 cm / 9-inch springform pan with butter and add parchment paper to the bottom of the pan.
Melt the butter and chocolate chips together in the microwave or over a double boiler until smooth.
200 g dark chocolate chips, 115 g salted butter
Add the cocoa powder, instant espresso powder, vanilla extract and with a rubber spatula mix it together. Set it aside while making the meringue.
3 tablespoon dutch process cocoa powder, 1 ½ teaspoon vanilla extract, 2 tablespoon instant espresso powder
Separate the egg yolk and egg white. Add the egg yolks in a bowl and set it aside for later. Add the egg white to a mixing bowl for your stand mixer, using the whisk attachment, or electric hand mixer.
5 large eggs
Whisk the egg whites, increasing gradually to medium high speed. Once the eggs looks frothy, whiter with larger air bubbles, then gradually add the granulated sugar.
150 g granulated sugar
Continue beating on medium high speed until its medium stiff peaks. Once medium stiff peaks, turn off the mixer and set it aside.
Add all of the egg yolks to the chocolate mixture and with rubber spatula mix them in until combined. Then add the egg whites in 3 parts. First add a third of the egg white. With the rubber spatula gently fold it together with the chocolate until almost fully combined. Repeat with the other third and again for the last addition. For the last addition it should be fully incorporated and no streak of the meringue or chocolate left.
Add the batter to the prepared spring pan, and gently even it out, and bake for 28-30 minutes or until a knife or toothpick instead in the middle comes out clean. Let it cool down completely on a wire rack before removing from the pan. Because of the meringue, the batter will puff up while baking and deflate when cooling down, giving it a nice soft crackled top.
Dust it with powdered sugar and serve with ice cream or a dollop of whipped cream.
powdered sugar for dusting, 125 ml heavy cream