In a sauce pan, combine sugar, egg, lime juice, and sauce. Whisk until blended. Add butter. Cook over medium heat, stirring constantly until mixture is thick and bubbly. Remove from heat, transfer to a bowl, and refrigerate until cool
In a large bowl, beat whipping cream and powdered sugar until peaks form. Fold whipping cream into chilled key lime curd. Cover and chill while cream puffs are baking.
In a medium sized sauce pan, bring water and butter to a simmer over medium heat. Add flour and with a wooden spoon, stir very quickly in one direction until the flour has absorbed all liquid. Cook for an additional 1-2 minutes. Transfer the dough to a mixing bowl fitted with a paddle attachment. Allow the dough to cool 4-5 minutes. With the mixer running, add the salt and eggs, one at a time, until everything is completely combined. Spoon the dough into a piping bag fitted with a large round tip.
Pipe 2 inch round mounds onto a parchment or silicone covered cookie sheet. Using wet fingers, tap down the point at the top of each mound. Bake at 425 degrees for 10 minutes. Reduce heat to 350 degrees and continue baking for 30 minutes. Remove from oven and allow to cool completely before filling.
Spoon chilled filling into a piping bag fitted with a small filling tip. Using a knife, split each cream puff without cutting completely through. Fill the cavity of each puff with key lime cream. Dust with powdered sugar and serve.