makes two crusts
Sift flour on pastry board. Form well in center of flour. Drop in egg yolks.
Blend in butter pieces with pastry blender or fork until mixture resembles coarse meal. Mix in sugar, vanilla, and zest.
Gradually blend in milk, tbsp by tbsp, until dough holds together.
Gently knead into ball. Do not overwork.
Use immediately; or divide if you prefer, wrap in plastic wrap, freeze until day before use, and thaw overnight in fridge.