Homemade citrus curd -- a mixture of eggs, sugar, butter, and orange and lime juices -- adds tangy flavor to this mousse.
Make citrus curd. Prepare an ice-water bath; set aside. Cook egg yolks, egg, 3/4 cup sugar, and juices in a medium saucepan over medium heat, whisking constantly (be sure to reach sides and bottom of pan) until thickened, 5 to 7 minutes. Remove from heat.
Whisk in butter 1 tablespoon at a time. Set pan in ice-water bath; whisk until cool, about 5 minutes. Pass curd through a sieve into a medium bowl. Press plastic wrap directly onto surface to prevent a skin from forming. Refrigerate until set, 30 to 45 minutes. Whisk cream and 2 tablespoons sugar until stiff peaks form; refrigerate.
Whisk one-third of whipped cream into curd. Gently fold in remaining whipped cream. Divide among serving bowls; refrigerate until ready to serve. Dust with cinnamon; garnish with citrus.