I adapted the recipe from this site Creative Kitchen Adventures
3 cups powdered sugar
2/3 cup cocoa powder
3 egg whites (I actually used egg substitute and it worked okay)
1 Tablespoon vanilla extract
4 oz chopped Bakers chocolate
Preheat oven to 350
Mix together dry ingredients
Add in vanilla and egg substitute
Pour into a pizza pan lined with tin foil and sprayed with pan spray.
Bake for approximately 20-30 minutes until top is cracked and center is still a bit gooey.
After it has cooled you can let the kids decorate it with frosting. I colored the frosting various colors and split it into 3 so they each got a separate "working space" on the cookie.