In a saucepan combine the lime juice, 1 1/2 cups of sugar, egg yolks, whole eggs, and butter and whisk to combine. Cook over medium heat, whisking constantly, until mixture comes to a boil, about 10 minutes. Remove mixture from the heat and strain through a fine mesh sieve into a clean bowl. Put bowl in an ice bath and place plastic wrap directly on top of the lime curd. Refrigerate until thoroughly chilled, stirring occasionally, at least 1 hour and up to 2 days.

Place 2 1/2 cups of the heavy cream and confectioner's sugar in a large mixing bowl and whip to soft peaks. Add all but 3/4 cup of the lime curd to the heavy cream and fold gently but thoroughly to combine.

Place 8 ring molds onto a parchment-lined baking sheet and divide the mousse among the molds. Freeze until firm, at least 4 hours.

When ready to serve, place the frozen mousse on dessert plates and allow to warm for 4 to 5 minutes before attempting to remove the ring molds. In a small bowl combine the creme fraiche with the remaining 1 1/2 tablespoons heavy cream and stir to combine. Drizzle some of the reserved lime curd around the mousse (if you have a squirt bottle, place the lime curd in a squirt bottle and drizzle decoratively around the plate) and garnish the mousse with a dollop of the creme fraiche mixture.