I made puff pastry dough. I rolled it out and cut into 8 rectangles. Then I put a stick of chocolate in the middle of each piece and rolled the dough to form a semi-cookie. As I put them in the preheated oven (200 C), the butter melted and cookies were swimming in the butter! Is it normally so? If not, how should I avoid this problem? I thought preheating the oven would help but it did not.