Start by melting the semisweet chocolate in a double boiler over simmering water, stirring occasionally until smooth, or use a microwave-safe bowl in 20-second intervals.
In a separate bowl, whisk the egg yolks with 1 ½ teaspoons of sugar until pale and creamy, about 2-3 minutes. Add the vanilla extract and coffee extract, mixing until combined.
Gradually fold the melted chocolate into the egg yolk mixture until well combined, being gentle to maintain airiness.
In another bowl, beat the egg whites with a pinch of salt until stiff peaks form.
Carefully fold the beaten egg whites into the chocolate mixture in three additions using a spatula.
Divide the mousse into serving glasses or bowls, cover, and refrigerate for at least 2 hours, or until set.
When ready to serve, garnish with fresh raspberries, mint leaves, and a dollop of sweetened whipped cream if desired.
