Heat oven to 400 degrees F. Unfold crust; press into bottom and up sides of 9-inch tart pan with removable bottom. Trim excess; prick bottom with fork; line tart shell with foil. Fill with pie weights or beans.
Bake in 400 degree F oven 15 minutes. Remove from oven; remove foil. Brush crust with egg white. Bake 8 minutes or until golden brown.
Boil leeks in water 5 minutes. Drain; squeeze out water.
Heat butter in nonstick skillet. Add garlic; cook for 2 minutes. Add leeks; cook for 5 minutes.
Whisk together eggs, half-and-half, salt and pepper in a bowl.
Sprinkle cheese over bottom of crust. Evenly distribute leeks over cheese. Slowly pour in egg mixture.
Bake in 400 degree F oven 30 minutes or until custard is set. If edges begin to brown too quickly, cover with foil. Makes 8 servings.