Roughly 3 hours out from serving, make the curd. Zest two of the clementines and place it in a small saucepan. Add the juice of all 5 of the clementines and the juice of one lemon. Whisk in the sugar and the salt and place over medium-low heat.
While the juice mixture is heating, whisk the cornstarch into the eggs and egg yolks until pale yellow. Add a ladleful of the hot juice mixture to the egg mixture, whisking constantly. Repeat with another ladleful and pour the resulting mixture into the saucepan.
Cook the curd until it's thick enough to readily coat the back of a spoon. Remove the curd from the heat and add the butter, whisking until it melts completely and is fully integrated.
Transfer the curd to a bowl and wrap tightly with plastic wrap. Chill for 2 hours or until ready to serve.