I made macsmom's Tropical Dreams cake last night. I want to make a tropical flavor for the top layer of a cake I making for next weekend. I decided I should try it first. I had to make a few changes because I couldn't get some of the ingredients but it was mostly flavor stuff like a different flavor yogurt and I didn't have and couldn't by any pina colada extract but nothing major. I put it in a 6" pan filled a little more than 1/2 way and made some cup cakes with the rest of the batter. When I tested the cake after 30 min it was not done so I left it in and test again in 5 more min. The cake tester came out clean the cake was a nice golden color so I took it out of the oven. When I went back in the kitchen later it had fallen, big cavity in the center. The cake just wasn't baked in the center. I used a cone it the middle because I was afraid of it not baking through. Can someone give me some advise about what to do to prevent this from happening. I baked it at 350. Should I use a cooler oven for more time, the cake was so under baked in the center I'm sure it I left it in for as long as it would have taken the edges would have burned. And why did my cake tester come out clean. I want to give it another try today but don't know what to do to prevent the same problem. I had this happen to a 14" layer once but putting the core in prevented that again.