Chocolatissimo

Preheat the oven to 300 degrees F (150 degrees C). Grease a 9-inch springform pan with butter; line the bottom with parchment paper.

Place chocolate, 1 ¼ cups butter, and coffee granules in the top of a double boiler over simmering water. Stir occasionally, scraping down the sides with a rubber spatula to avoid scorching, until melted and smooth. Cool to lukewarm.

Beat egg yolks and sugar together in a large bowl with an electric mixer until thick and lemon-colored. Fold into chocolate mixture until well combined; set aside.

Beat egg whites in a large glass or metal bowl until stiff peaks form. Fold ⅓ whites into chocolate mixture, then quickly fold in remaining ⅔ whites until no streaks remain. Pour ⅔ mixture into the prepared pan; cover and refrigerate remaining ⅓ batter.

Bake in the preheated oven until filling is just firm in center, about 40 minutes. Cool, then remove cake from the pan, and refrigerate for 1 hour.

Spread remaining ⅓ batter over cooled cake; refrigerate 8 hours to overnight.