1. In a saucepan over medium-high heat, bring the cream to a boil. Remove from the heat and stir in the chocolate and egg yolks until chocolate has melted. Stir in Grand Marnier. Set aside until just warm.
2. Stir in butter until melted (mixture will be very thick).
3. Divide the mixture among 12 small glasses and cover with plastic wrap. Refrigerate until firm (2-4 hours or up to overnight). Garnish with 1/2 teaspoon zest. Serve.