Whisk together the egg yolks and sugar in a medium bowl, until pale and fluffy, about 2 minutes. Set aside.
Warm 1 cup of heavy cream and the salt in a saucepan over medium heat. Stirring occasionally, heat until the mixture reaches a temperature of 160°F and bubbles start to form around the edges.
Temper the egg yolks by very slowly pouring the hot cream mixture while whisking constantly. Pour this mixture back into the saucepan and heat, stirring frequently, on low heat to a temperature of 160°F.
Remove from heat and add the chocolate, Grand Marnier, vanilla extract and orange zest. Stir until the chocolate is melted and smooth. Cover and chill, stirring every 10 minutes until no longer warm, about 30 minutes.
Whip the remaining 1 ½ cups of heavy cream to stiff peaks. Fold into the chocolate mixture until combined. Spoon into cups and chill for 2 hours. Top with some whipped cream and orange zest.
Notes
You want really good quality chocolate as it tastes better and melts well.
Don't skip tempering the eggs or you will have scrambled eggs.
If the chocolate doesn’t melt fully in the cream mixture, just return the saucepan to low heat and stir to melt.
Use a chilled bowl to get really fluffy whipped cream.
Don't overfold the mixture when adding the whipped cream or it will lose its airiness.