Cream 3/4 lb softened butter and 1 cup powdered sugar together.
Sift 3 cups flour, 1/4 cup sugar and 1/2 teaspoon salt, then add to mix.
Add 1/2 teaspoon vanilla, blend.
Wrap dough in wax paper, chill 4-6 hours in refrigerator.
Put in two 9" tart pans (1 1/2" high) an bake for 27-30 minutes at 325 degrees F. [time is adjusted for silicone pans].
In a food processor or blender, combine the lemon zest (7 med. sized lemons worth) with 1/4 cup of the sugar and process until fine and moist, several minutes.
In a medium-sized bowl, combine the eggs, the 3/4 cup sugar, and the zest mixture. Whisk briskly until well blended. Stir in freshly squeezed lemon juice. Place the bowl over a saucepan half-filled with slowly simmering water and stir until the mixture thickens enough to lightly coat the back of a wooden spoon, 6 to 8 minutes.
Stir in the butter, a piece at a time, mixing until melted and smooth. Strain through a fine-mesh sieve. Immediately pour the lemon butter into the tart shells and set aside. The filling will set as it cools. Let cool completely before serving.
Just before serving, lightly dust the edges of the tarts with powdered sugar.