Step 1

In a large nonstick skillet, cook onions in butter over medium-low heat until very tender, 30 minutes. Meanwhile, preheat oven to 450°. Line unpricked crust with a double thickness of heavy-duty foil.

Step 2

Bake crust 6 minutes. Remove foil; cool on a wire rack. Reduce oven setting to 425°.

Step 3

Spoon onions into crust. In a small bowl, whisk egg substitute, milk, salt and pepper; pour over onions. Bake until a knife inserted in the center comes out clean, 30-35 minutes. Let stand for 5-10 minutes before cutting.