Thaw spinach and drain well.
Roll out half the pastry and line 9-inch pie pan.
Separate 1 egg, then brush egg white on pie shell.
Pour excess white into large bowl; add yolk and remaining 2 eggs; set aside.
In skillet sauté onion in butter until tender.
Meanwhile beat eggs; stir in cheese, spinach, salt, pepper and onion.
Turn into pie shell. Roll out remaining pastry, fit over pie and crimp edge.
Bake in preheated 425° oven 30 minutes or until crust is golden.
Cool on rack 10 minutes. Cut in wedges to serve.
Servings: 6