Preheat oven to 325°F (160°C). Grease a small springform pan or 6-inch baking dish.
Make the crust: Mix crushed crackers, butter, and sugar. Press into the bottom of the pan. Bake for 8 minutes. Let cool.
Prepare the filling: In a bowl, blend ricotta and cream cheese until smooth. Add sugar, egg, flour, lemon zest, lemon juice, and vanilla. Mix well.
Pour the filling over the cooled crust and smooth the top.
Bake for 35–40 minutes, or until the center is just set.
Let it cool completely, then chill in the fridge for at least 2 hours.
Serve cold, with lemon slices or berries if desired.