Preheat your oven to 325°F (160°C). Line a 12-cup muffin tin with paper liners.
In a medium bowl, mix together the graham cracker crumbs and the melted butter. Press into the bottom of each muffin liner.
In a large bowl, beat together ricotta cheese and granulated sugar until smooth. Mix in eggs one at a time, then stir in lemon juice, lemon zest, and vanilla extract until just combined.
Spoon the ricotta filling evenly into each muffin cup, over the crusts. Fill almost to the top.
Bake for 20-25 minutes, until edges are set but centers still slightly jiggle.
Turn off the oven and leave the muffin tin inside with the door slightly ajar for 30 minutes. Then, cool completely at room temperature.
Refrigerate for at least 2 hours, or preferably overnight. Serve chilled, garnished as desired.