Dorie Greenspan doesn’t know why people tell her that baking is difficult. After all, she already created the recipe. “I did the work,” she laughs, “Just follow the recipe.” Greenspan has created 300 cookie recipes and they are in her new book “Dorie’s Cookies.” The cookbook author and baking guru came to Sherry B’s Dessert Studio in Chappaqua, N.Y., recently to talk about her new book and share tips for making her favorite cookies. The woman who once measured ten cups of flour in metric to come up with an average of 136 grams per cup, says precision is not so important. “There’s a margin of error,” Greenspan says. “It’s not as precise as we all thought.” Recently she discovered that she and her recipe testers had been using different methods of measurement for the same recipe. And all the cookies tasted great. It’s a thought that helps Greenspan “sleep better at night.” She firmly believes in the metric system. As she spoke, members of Sherry B’s studio passed around plates of adorable little cookies – jam thumbprint, …