Line muffin tins with 15 cupcake papers.
In a small bowl, combine the graham cracker crumbs and sugar.
Stir in the melted butter. Press about a tablespoon of crumb mixture into the bottom of each cupcake paper.
Preheat oven to 325 F. In a blender or food processor, combine the cream cheese, ricotta cheese, sugar, egg yolks, heavy cream, lemon juice and zest. Blend until creamy. This can take a few minutes.
In a separate bowl, whip eggs whites until stiff peaks form. Its helps to chill the bowl, beaters, and white before whipping.
Gently fold the egg whites into the cheese mixtures.
Spoon into the cupcake paper, filling them up to to 1/2 inch of the rim.
Bake for 10-15 minutes until just set. Don't over bake.
Turn off the oven and open the door and let them cool for one hour before taking them out of the oven. Chill.
When ready to serve, top with whipped cream and a strawberry if desired.