I have this awesome recipe for ginger cookies that I've made a million times, although not recently. I made a batch last night and after only about 8 minutes in the oven (recipe calls for 12-15 mins total) the bottoms were burned. I even had to throw away one of my cookie sheets because the sugar on the cookies had caramelized and stuck to the sheet (recipe calls for ungreased cookie sheet). My question is, what could be causing this? Oven temp? Old, crusty, gross cookie sheets? Should I have greased the sheet, despite the directions? I have to make more cookies for Christmas and I don't want to ruin them all. Any suggestions?