In a food processor fitted with a steel blade, add the flour, 2 tablespoons sugar, and salt. Pulse a couple of times to combine. Cut the 8 tablespoons butter into pieces and add to the processor, then pulse until the texture is like very coarse meal.
Pour in 1 tablespoon of the milk, pulsing until the dough comes together in a ball. Add more milk, a little at a time, as needed (you might not use it all).
Shape the dough into a disk, cover with plastic wrap, and refrigerate for at least 30 minutes.
After chilling, preheat the oven to 350°F. Roll out the piecrust, and gently press into an ungreased 9-inch tart pan. Trim excess crust off the top. Prick it all over with a fork, and bake for 10-15 minutes, or until golden brown. Let cool.
To make the filling
Zest lemons to get 2 tablespoons of zest, then juice the lemons to get about 3/4 cup juice.
Whip the eggs and 1 cup sugar in the bowl of an electric mixer at medium speed. Gradually add the lemon juice and zest.
Pour the filling ingredients into a medium saucepan, add the butter or margarine, and cook over medium heat, stirring constantly, being careful not to boil, until the lemon thickens into a curdlike custard, about 5 minutes.
Pour filling into the baked crust. Chill until firm, at least 4 hours.