Spanakopita Spinach Pastry

Mix flour and butter in a glass bowl and whisk in milk.
Microwave sauce 1 minute at maximum power. Stir and cook another minute at 70% power. Cool, then stir in eggs one at a time until sauce is smooth and creamy. Set aside.
Meanwhile, thaw and drain spinach in a colander, pressing down to remove excess water. Heat oil in a saucepan and add green onions, spinach and dill. Season with salt and pepper and simmer for 5 minutes. Add Parmesan, mixing well. **Feta can be substituted for Parmesan.
Cut phyllo dough in two. Roll the dough out into two 8 1/2» x 10 1/2» (20 cm x 25 cm) rectangles and line the bottom of a baking pan with one. Spread spinach mixture over dough and cover with second rectangle. Crimp edges all around pan. Make 1» (2 cm) cuts.
Baste top crust with egg white and bake 40 minutes in a 400°F / 200°C. Serve with egg sauce.