In a large mixing bowl, combine butter and sugars. Mix until well blended.
Add egg substitute and vanilla.
Fold flour mixture into sugar mixture until combined. Fold in chocolate pieces.
Divide batter evenly into 8 4-ounce greased ramekins. Cover and refrigerate 4 hours or up to 2 days.
When ready to bake, remove ramekins to sit at room temperature for 10 minutes. Preheat oven to 350 degrees F. Bake for 18 minutes.
Sprinkle with powdered sugar and serve.