In small saucepan, mix egg yolks and sugar on low until sugar is dissolved. Set aside. Chop bittersweet chocolate so that it is fine. Add to the saucepan and mix until the chocolate is melted. Then add unsweetened cocoa powder until the mixture is melted and smooth. Set aside and cool. In bowl, mix heavy cream until soft and light. Mix half of the whipped cream with the chocolate mixture. Mix. Slowly add the rest of the heavy cream. Chill the mousse for two to three hours. When ready to serve add raspberries