HELP! My cake completly sank and then fell apart

Hi, and sorry about your disasters. We need a little more information.

First, are these recipes you have used before successfully? If so, the first place I would look for a problem is with your oven temp. It can go out of calibration in one baking session. Get an independent thermometer and check it. Next, was an ingredient changed. For example, my very expensive chocolate cake ($30.00/lb chocolate in the batter) sunk slightly two times. This is a recipe I use all the time. I researched it and found that because I was out of 70% chocolate, I used 60% instead. That difference took my batter out of balance.

Batters should go in the oven asap for best results, some more than others. The leavening reacts two times, once when the liquid is introduced, and the other when heat is introduced. The first reaction can "die" if you wait too long to introduce the heat. They should be baked within 1/2 hour if not immediately.

If these are new recipes, they may not be balanced recipes. The strips are not your problem. I use them on 6 inch cakes when I'm going for a three inch tall cake. I wrap it all the way up the sides. On a 2 inch tall cake, it really is unnecessary, but won't fail your recipe.

So let us know if it was a new recipe. If it was, post it. If you used an off brand butter (more water content), reduced fat ingredient, etc., look at your changes. New mixer? Being tired (this is a big one). Let us know.

If I can: sooo much milk and sugar! I'd have halved sugar (but don't know how sweet do you like your cakes), and milk - or even 1/3 of milk you added if you use cocoa powder and oil instead of chocolate, +1 oz chocolate + 1 egg, even 2 + 1 tsp baking powder. (Sorry, I'm not good with imperial system, hope I calculated everything right).

I had some leftover batter (chocolate cakes) in the fridge from Wednesday - it usually never happens but took some last minute orders and had a lot of decorating to do, so I left it there. It was enough just for one 6'' layer, baked it yesterday and it was so good. I was actually quite surprised. I'd normally use all batter immediately exactly for reasons scp mentioned.

Let's see what others will advice. Did you use this recipe before?

Just to add a note here: I often have leftover batter or dough and have never had a problem refrigerating anything for future use. And when my time is tight, I'll make the batter ahead and bake it off another day. Again, with no problems. There may be a few fussy recipes out there that can't tolerate such behavior, but if one like that ever found it's way into my kitchen I'd toss it. (Sorry, I have no tolerance!)