Preheat oven to 350°.
Combine first 5 ingredients in a small bowl,
stirring to form a streusel. Set aside.
Place potatoes in a Dutch oven;
add water to cover.
Bring to a boil; cover, reduce heat,
and simmer 30 minutes or until very tender.
Drain well; mash in a large bowl.
Stir in 1 cup streusel, granulated sugar,
vanilla, egg white, and milk.
Spoon into a 2-quart casserole coated with cooking spray;
top with remaining streusel.
Bake at 350° for 45 minutes.
Yields: 8 servings (serving size: 3/4 cup)