In a small heatproof bowl, combine the yuzu chocolate and butter. Set the bowl over a pot of barely simmering water and stir continuously until the chocolate and butter have melted, and they are smooth. Remove the bowl from heat but leave the pot simmering on low.
1 Cup Yuzu Chocolate, 6 tablespoon Unsalted Butter
In a medium heatproof bowl, whisk the egg yolks and sugar together. Set the bowl over the pot of barely simmering water and whisk continuously for about 5 minutes, until the mixture turns pale and becomes slightly stiff. Then, remove from heat and set aside.
4 Large Egg Yolks, ¼ Cup Granulated Sugar
Add the melted chocolate and butter into the egg mixture, stirring to combine. Stir for a few more minutes to allow the mixture to cool then set aside until it cools to room temperature.
In a large bowl, whip the cream to soft peaks. Whisk ¼ of the whipped cream into the cooled chocolate mixture. Use a silicone spatula to gently fold in the remaining whipped cream until fully mixed in.
1 Cup Heavy Cream
Divide the mousse among four 6-ounce ramekins and refrigerate until it has set, about 1 hour.
Add a dollop of whip cream on top with a bit of lemon zest for garnish!
Lemon Zest and Extra Whipped Cream for Garnish