Preheat oven to 350°F. Spray 3 mini muffin pans with cooking spray. (I like the kind with flour in it for these pies.) This makes about 40-42 pies.
Unroll your pie crusts and cut 2.5” circles with a cookie cutter or jar. Press each carefully into each mini muffin cavity.
Re-roll dough as needed. Chill until filling is ready.
Whisk melted butter and sugar until smooth, then whisk in eggs until the mixture is a rich yellow, about 30 seconds.
Whisk in the salt, lemon zest, vanilla, lemon juice, milk, and flour, one at a time, whisking until smooth.
Fill each pie crust with 1tablespoon of filling. You may have just a bit of filling left over.
Bake pies for 17-20 minutes until the tops are no longer wet. The crust will just be very lightly brown. (I like to place my muffin tins on a cookie sheet before baking, for easier handling and less spilling.)
Cool pies completely before removing from pans. They should pop out easily with the help of a knife. Dust with powdered sugar before serving, if desired.