1. Make the crust binder: In a medium bowl, stir the graham cracker crumbs together with the warm melted butter until the mixture holds together when pressed.

2. Whip the filling: In a separate bowl, use an electric mixer to beat the softened cream cheese and powdered sugar until completely smooth. Pour in the sweetened condensed milk and continue beating until combined.

3. Add the lime: Mix the key lime juice, granulated sugar, and lime zest into the cream cheese mixture until the texture becomes silky and the lime flavor is evenly distributed.

4. Chill briefly (optional): Pop the filling into the refrigerator for about 1–2 hours if you want it firmer for piping; if you don’t mind spooning, you can skip this step.

5. Layer the jars: Spoon or pipe a layer of graham crumbs into the bottom of eight 8-ounce jars. Add a layer of the lime cheesecake mousse, then repeat, finishing with a final layer of mousse on top. Seal the jars with their lids if using.

6. Set in the fridge: Refrigerate the parfaits for at least 3 hours (overnight is even better) so the filling firms and the flavors meld.

7. Finish and serve: Remove lids, top each parfait with a dollop of whipped cream, and garnish with extra lime zest before serving.

Tip: For cleaner layers, chill the filling until slightly firm before piping; for a pie version, press the crumb mix into a 9-inch dish and pour the filling over it, then chill until set.