I have always been paranoid of over-cooking my cakes and having them be dry. I tend to lean the other direction toward under-baking.

This particular cake was terribly under baked and I don't understand it.  

It is a 7" cake. It was supposed to be marble, but as you can see, it mostly just mixed together (that is another issue that I fixed when I re-baked the cake).

I used parchment lined pans and an Ateco heating core in the center of the cakes. I usually use baking strips on the outside of the pans, but forgot to put them on. 

I know that the baking strips make a difference because when I re-baked I used them and the cake was better, but not perfect. There was still a very small area in the center that was not baked completely when I torted it.

Here's my problem.....I checked the cake with wooden toothpicks and pulled the cakes out when the toothpicks came out clean....not with a few little crumbs on them, but clean. I even checked in a couple of places. The tops were springing back like they should and the sides were pulling away from the pans.  WHY where they NOT done? Why would the toothpick come out clean if it was so underdone (see photo below).

I'm so frustrated because I don't know how to fix the problem.  Can anyone help me?

AI cannot understand what your picture is of. Did you cut the cake in half horizontally? What are all the holes?

It almost looks burnt on the edges.  Rather than it being undone in the center, could it have fallen and give the appearance of underdone?

I agree, I think the cake is more overdone 

Either way, you should check your oven temp with a separate oven thermometer.

It is not burned. That is dark chocolate cake that you are seeing.

It didn't fall, I had to cut a slight dome off to level.

This picture is of the cake sliced through them middle horizontally to add filling.

I have no idea what the holes are, unless they were air holes. I always tap my pans on the table to try to remove air bubbles before I put them in the oven, so I'm not sure what that is about.

I forgot to mention that this was a recipe that I had never tried, but gets good reviews. It was Martha Stewart's marble wedding cake recipe. I did have to make a change from using half heavy cream and half milk to all milk because I didn't have the cream on hand. It made the batter really runny, so the vanilla and chocolate parts ended up blending together instead of marbling.

I tasted the dome that I cut off and it tasted great, was not overcooked or dry. I just want to know if anyone else has had their cake testers come out clean and the cake was still basically raw in the center.

Are you using a single batter, dividing it, and adding chocolate to part of it, OR are you using two different recipes one white, one chocolate?

I am using a single batter, separating it, and adding chocolate to it. I had to triple the recipe for the cakes I was doing and had a little left over.

Here's the recipe I used (except for the cream part, I used all milk):

http://www.marthastewartweddings.com/224423/marble-cake

I'm stumped.  Bad recipe?  A 7 inch really shouldn't have that much problem, especially with a heating core.  And I think the air holes, tunnels can be caused by overmixing.  At least that is what we were taught in 4-H many years ago.

Even the little guy in the picture looks like the edges are really browned.

ADid you flip it out of the pan when it was still hot? Maybe it was cooked but it got compressed after it was cooked, before it was cool enough to set.

I'm familiar with this. It isn't under baked. It's a problem with your leavening, I'm 100% certain. The tell tale sign is the deep tunneling wholes in the center. If it was under baked the wholes would have collapsed and you wouldn't see them at all. Instead the batter did complete baking and it isn't falling in on itself.

Usually it's too much leavening that causes this. Too much leavening and the tiny air bubbles in a cakes structure over pop as it bakes collapsing the batter on itself, making a dense cake center. Usually it's a balance problem in the recipe itself. Too much liquid, too much acid, too many eggs, or too much baking soda.

If the recipe normally works for you and this just happened as a surprise it can be that you grabbed for the baking powder and accidently used baking soda.

Ah, I just re-read one of your posts when I checked the recipe. 

"Here's the recipe I used (except for the cream part, I used all milk):"

That's where you went wrong. You can't use all milk, milk doesn't have as much fat as the cream. Believe it or not, that small chemical difference is all that it takes to change the chemistry of that batter. All milk made the batter leaner and wetter so the tiny air pockets collapsed on each other as the cake baked. 

All that chocolate came from ONE cup of batter mixed with chocolate?  Did you stir the chocolate mix into the batter by hand, or did you use your mixer?  Given that the chocolate is concentrated in the center and it domed, you may have over mixed the chocolate part, or mixed it too vigorously.

I'll agree that using the milk rather than the cream would have upset the fat balance and led to issues.

I will also say that I would NEVER compress the dome on my chocolate cakes, especially not while they're still warm.  The result would be a dense soggy mess. 

I also note that the recipe says to allow the cakes to cool completely in the pan, are you sure the 12 minutes was long enough? 

A similar thing happened to me a few weeks back. I checked with a stick and it came out dry, but once it had cooled and I sliced it it wasn't baked in the center. I figured out that it was because I dropped the oven door (by accident) during baking. Maybe something similar might have happened to you??