Oh... damn... I did everything right. It's the blooming heat seals. The oven is so old, they don't make the model any more. If I could, I'd replace them. *sigh*Mewmew - collapsed center and still gooey, that's a classic sign of not being baked through, and since you're using a boxed mix and following their directions, I'm sure you left it in for the right amount of time and used the right sized tin, that's really pointing to your oven being out of whack. Believe me, I've been through the same thing.