Beat egg yolks in the bowl of a stand mixer with the whisk attachment for 3 minutes until thick. Gradually add the sugar while beating.
Heat 1 cup of cream in a small sauce pan until hot. With the mixer on, stream 1/2 of the hot cream into the eggs. Once combined, pour the mixture into the pot with the remaining 1/2 cup cream. Turn the heat to low and cook until thick, stirring constantly (5 minutes).
Mix in the vanilla and then add in the chocolate in 3 batches, stirring over low heat until melted and smooth.
Pour the mix into a large bowl, cover, and place in fridge for 1.5-2 hours, stirring every 20-30 minutes. Once no longer warm, remove from the fridge and whip up the remaining 1 1/2 cups heavy cream to stiff peaks. Fold the cream into the cooled chocolate mixture.
Pipe or spoon the mouse into small glasses. Cover and place in fridge until ready to serve.
Garnish with fresh whipped cream and shaved chocolate.