There are two reasons that could of happened. 1. HANDLING THE DOUGH: When forming the cookie ball, don't press the dough together too much. Try to keep it airy. Only press it together enough for it to stay together. 2. CHILL THE DOUGH BEFORE BAKING: Once the dough is formed into balls and placed on a cookie sheet lined with parchment paper, slide the cookie sheet into the refrigerator for 2½ hours. CHILLING COOKIE DOUGH CONTROLS SPREAD. CHILLING COOKIE DOUGH BEFORE BAKING SOLIDIFIES THE FAT IN THE COOKIES. AS THE COOKIES BAKE, THE FAT IN THE CHILLED COOKIE DOUGH TAKES LONGER TO MELT THAN ROOM-TEMPERATURE FAT. AND THE LONGER THE FAT REMAINS SOLID, THE LESS COOKIES SPREAD.