In a heavy-bottomed medium saucepan, mix together sugar, flour, and salt.
In a separate mixing bowl, beat together the egg yolks and milk. Whisk the egg mixture into the dry ingredients in the saucepan. Continue whisking over low heat until the mixture coats the back of a spoon and is smooth and thick.
Remove from the heat and stir in the butter and vanilla. Cook's Note: Add any variations at this point.
Allow the mixture to cool and pour into the baked pie shell. Chill the pie completely and top with fresh whipped cream or other desired topping.
Preheat the oven to 425 degrees F.
In a mixing bowl, mix together the flour and the salt; cut or work the butter into the flour with your fingers or a pastry blender until you have large pea sized chunks scattered throughout. Alternatively, pulse the dough in a food processor, or mix in a stand mixer with the paddle attachment on low speed.
Add the ice water slowly while stirring with a fork, or in the food processor or mixer, until just combined. Be careful not to overwork the dough. Divide the dough into two disks, flatten and refrigerate each for at least 15 minutes.
Roll out one chilled pie dough to fit a 9-inch pie plate. Reserve the second pie dough disc for another use. Transfer dough to pie plate, pressing the dough lightly into the plate; trim the edges. Dock the dough with the prongs of a fork evenly over the bottom of the pie plate. Line the docked dough with aluminum foil and fill with pie weights or dried beans.
Bake the pie crust until the edges are brown and golden, about 15 minutes Remove from the oven and remove the weights. Return crust to the oven to finish baking for another 5 minutes.
Banana Cream Pie: Make the basic filling and cool. Slice 3 to 4 bananas into the bottom of the prepared pie shell. Pour the cooled basic filling (or chocolate filling) on top. Coconut Cream Pie: Stir 1 cup flaked coconut into basic filling just before pouring into pie shell. Sprinkle toasted coconut on top of the whipped cream for a beautiful and tasty presentation. Butterscotch Cream Pie: Substitute 3/4 cup firmly packed brown sugar instead of white sugar in the basic filling recipe, and increase the butter to 3 tablespoons. Cook in the same manner as the basic filling. Peanut Butter Chocolate Cream Pie: Make the basic filling and add 1/4 cup creamy peanut butter and 3/4 cup good quality chopped semi-sweet chocolate to the hot filling in the pan. Stir until the chocolate is completely melted.