Beat the egg yolks in a large bowl with a hand mixer on medium-high speed for 3-4 minutes until they have turned a light yellow color and thickened. Gradually add the sugar while beating, then set aside.
4 large egg yolks, 1/4 cup granulated sugar
Heat 1 cup of the cream in a medium saucepan over medium heat just until hot and small bubbles begin to form around the edges of the pan. Do not let the cream boil.
2 1/4 cups cold heavy whipping cream
Remove from heat and slowly pour half of the hot liquid into the egg yolks while whisking to gently raise the temperature of the eggs without scrambling them.
Add the tempered egg yolks to the saucepan and return to medium-low heat. Continue to cook and stir for 3-4 minutes until the mixture is thick enough to coat the back of a spoon and reaches 160°F on a thermometer.
Add the chopped chocolate and stir with a sturdy spatula until it is completely melted. Stir in the vanilla extract. Let cool completely at room temperature (about 1 hour).
8 ounces chopped semisweet chocolate, 2 teaspoons vanilla extract
Once the chocolate mixture has cooled, beat the remaining 1 1/4 cups cream in a bowl with a hand mixer or a stand mixer fitted with the whisk attachment until it reaches stiff peaks. Add 1/3 of the whipped cream to the chocolate mixture, folding it in gently. Add the remaining whipped cream and fold this in as well.
Transfer the chocolate mousse mixture of a piping bag fitted with a large open tip and pipe it into eight 6-ounce glasses or dessert cups. You could spoon the mousse in if you prefer not to pipe, but the presentation is neater with piping.
Cover and refrigerate for 1-2 hours to set. Top with sweetened whipped cream, shaved chocolate, and fresh berries to garnish before serving.
shaved chocolate, sweetened whipped cream, fresh raspberries or sliced strawberries