01 - Set up a double boiler by placing a heatproof bowl over a pan of simmering water. Add the chopped dark chocolate and stir continuously until completely smooth and melted. Remove from heat and allow to cool for approximately 5 minutes until lukewarm.
02 - In a thoroughly clean, dry mixing bowl, whisk the egg whites with a pinch of salt using a hand whisk or electric mixer. Continue whisking until soft peaks form, then gradually sprinkle in the granulated sugar while beating. Whip until stiff, glossy peaks form and the sugar has dissolved.
03 - Lightly beat the egg yolks in a separate bowl. Slowly pour the cooled melted chocolate into the yolks, whisking constantly to prevent the eggs from scrambling. Mix until the mixture is completely smooth and uniform in color.
04 - Gently fold one-third of the whipped egg whites into the chocolate-yolk mixture to lighten it. Add the remaining egg whites in two more additions, folding with a spatula using a figure-eight motion until no white streaks remain. Take care not to overmix and deflate the air incorporated.
05 - In a chilled bowl, whip the cold heavy cream using a whisk or electric mixer until soft peaks form. The cream should hold its shape but still have a slight流动性 when the whisk is lifted.
06 - Gently fold the whipped cream into the chocolate mixture in three additions, using the same careful folding technique. Continue folding until fully incorporated and the mousse is smooth, airy, and uniform in texture.
07 - Divide the mousse evenly among 4 serving glasses or bowls, smoothing the tops with a spatula. Cover with plastic wrap and refrigerate for a minimum of 2 hours, or until the mousse is completely set and firm to the touch.
08 - Just before serving, arrange fresh strawberry halves on top of each chilled mousse. Dust lightly with powdered sugar using a fine-mesh sieve and garnish with fresh mint leaves if desired.