Melt the chopped semisweet chocolate in a double boiler or microwave-safe bowl until smooth. Set aside to cool slightly.
In a mixing bowl, whisk together the egg yolks, pinch of salt, vanilla extract, and coffee extract (if using). Pour in the melted chocolate and mix until fully incorporated.
In a separate bowl, whip the egg whites until soft peaks form. Gradually add the sugar while continuing to whip until stiff peaks form.
Gently fold one-third of the whipped egg whites into the chocolate mixture. Then, fold in the remaining egg whites until no white streaks remain.
Spoon the mousse into serving dishes and cover with plastic wrap. Refrigerate for at least 2 hours or until set. Garnish with fresh raspberries, mint leaves, and whipped cream, if desired.