Preheat the oven to 325 degrees F (165 degrees C). Grease a 6-cup muffin pan.

Mix graham cracker crumbs, sugar, and melted butter together with a fork in a medium bowl until combined. Measure a rounded tablespoon of the mixture into the bottom of each muffin cup, pressing firmly. Bake in the pre-heated oven for 5 minutes, then remove to cool. Keep the oven on.

Beat cream cheese, sugar, lemon juice, lemon zest, and vanilla together until fluffy. Mix in the egg.

Pour the cream cheese mixture into the muffin cups, filling each until 3/4 full. Bake at 325 degrees F (165 degrees C) for 25 minutes. Cool completely in pan before removing. Refrigerate until ready to serve.