Preheat oven to 350°.

Combine sweet potatoes, three fourths of the brown sugar substitute, milk, egg, melted margarine, and vanillia. Stir well.

Spoon the mixture into a shallow baking dish coated with cooking spray.

In a separate bowl, combine the flour and remaining brown sugar substitute. Cut in 1 tablespoon of margarine. Mix until crumbly. Sprinkle over the potatoes.

Bake for roughly 35 minutes, or until thoroughly heated.