I baked a 10" round cake with 6 cups of batter as the pan instructions state, using the "Darn Good Chocolate Cake" recipe from this site (which I have used before with success). I greased the bottoms and sides with cake release, and used a flower nail in the center (as a heat core).

During baking, my cake rose evenly until it got higher than the nail, then it began to peak in the center. I had to give the cake extra time until it tested done. As the cake cooled, the center sank, and the sides caved in making it look like a flattened hourgalss.

I tried again (this time I did not use my convection oven)...with the same results. What am I doing wrong?

Please help as I have a cake to deliver in 2 days! I don't want another flop!

if you're center is falling there are two common reasons
1) your baking soda/powder is bad
2) you aren't letting your cake cook long enough so it's not done