Step 1Heat the oven to 350 degrees. Prick the bottom of the tart shell lightly with a fork, line it with parchment paper or aluminum foil and fill it with pie weights (you can use dried beans and save them to use as weights the next time you bake). Place the tart shell on a baking sheet and bake until the rim of the tart is dried and set, about 15 minutes (time may vary depending on the dough or brand). Remove the weights and the aluminum foil and return the tart shell to the oven to bake until the crust is set but not completely baked through, about 10 minutes more.
Step 2Meanwhile, prepare the filling. In a blender, puree the lemon, sugar, butter, vanilla and eggs until smooth, 2 to 3 minutes. This makes about 3 cups filling. Pour the filling into the pre-baked tart shell until the filling almost reaches the top of the rim of the crust; you may not use all of the filling.
Step 3Place the tart in the oven and bake until puffed and golden and the filling jiggles only slightly when tapped, about 40 minutes. The filling will brown around the edges, but should not be overly brown in the center; if it begins to brown too quickly, cover the top lightly with aluminum foil and continue baking. Remove and cool on a rack.