In a medium saucepan over low heat, whisk together the lemon juice, sugar, and eggs until well combined. Stir continuously for about 10 minutes until it thickens. Remove from heat and stir in the butter until melted. Strain through a sieve and refrigerate until chilled.

Preheat the oven to 350°F (175°C) if you want a toasted crust. Pulse graham crackers in a food processor until fine crumbs, then mix with melted butter. Press into the bottoms of dessert cups, or refrigerate for 15 minutes if not baking.

Beat room temperature cream cheese and sugar with an electric mixer until smooth. Fold in the cooled lemon curd. Whip heavy cream until stiff peaks form, then fold it into the lemon curd mixture.

Pipe the cheesecake mousse into each dessert cup halfway, add a layer of lemon curd, then pipe more mousse on top.

Sprinkle with reserved graham cracker crumbs, cover with plastic wrap, and chill for at least 1 hour before serving.