Preheat oven to 325 degrees. Grease 9-inch square baking pan.
In a small bowl, whisk together flour, baking powder, and baking soda.
In a small saucepan, combine sugar, butter, and water. Bring to a boil over medium heat; remove immediately from heat. Stir in one cup of chocolate morsels and vanilla extract until chocolate is melted and mixture is smooth. Cool completely.
Whisk in eggs one at a time, beating well after each addition. Tip in flour mixture; quickly fold and blend just until ingredients are combined but batter is still lumpy. Stir remaining chocolate morsels into batter.
Pour batter into prepared pan.
Bake 30 to 35 minutes or until a toothpick inserted in center comes out clean. Transfer pan to a wire rack to cool completely