I am fed up with putting my failures in the bin. The problem is that they are cooked (or even overdone) around the edge but the middle is still raw. I know they are supposed to be gooey but this is not right. The top looks cooked - how do I get them cooked through without burning the top & edges. I use a fan oven if that is relevant. I am an experienced baker and can do most stuff without difficulty. Help please!