If your chocolate filled cookies spread out all over the baking sheet, there may be a few reasons. First, make sure your cookie dough is chilled enough to handle before baking. You should be able to pick it up and mold it a bit with your hands. Chill the cookies for a few extra minutes before baking if you're having trouble. Second, if you swapped the bread flour for all-purpose flour, your cookies may end up spreading more in the oven. Try freezing the cookies for 10-15 minutes before baking if you used all-purpose flour. Finally, don't forget the cornstarch. It can help keep the cookies from spreading in the oven.