Add the freshly squeezed lemon juice to a bowl, adding water if necessary to make up 1/4 cup.
Sprinkle the gelatin over the liquid, and let it react (or bloom), for about 5 minutes.
Add the cream, sugar, and lemon zest to a saucepan over a medium-low setting. Gently heat the mixture, stirring until the sugar has dissolved. It shouldn't get hotter than a low simmer.
Using a whisk, blend in the gelatin mixture, until all of it has dissolved.
Remove the saucepan from the heat, and stir in the Cointreau.
Divide the mixture between ramekins or glass bowls – you should end up with 4 to 6, depending on the size.
Place in the fridge, uncovered, and allow to set for at least 4 hours.
Once set, cover with plastic wrap, and allow them to chill overnight.