I used to make a gingerbread recipe of my Grandmother’s. I made it for years when I lived in Maryland, then I moved to Maine. For some reason, the gingerbread started to sink in the middle.
Everything was the same, same method, same ingredients. I tried different kinds of flour, I tried adding more baking powder, less baking powder, baking powder for leavening and soda for neutralizing the acidity in the molassas. I looked up different recipes, I must have spent years trying everything I could think of to keep it from falling. I had even resorted to using smaller pans and hiding the depression under a thick layer of fudgy frosting (a tradition with my family anyway, so who’s to argue with an extra layer in the center.)
Then last year (I’ve been in Maine for 13 years. Can you tell that this has been making me a bit crazy?), after baking a regular cake the words “beat for to aerate and develop the cake’s structure” came to me. You will find them in most of Rose’s butter cake recipes.
I added this thinking to my Grandmother’s very spare recipe, and guess what? The center doesn’t sink anymore. All the ingredients are exactly the same. I use the same method of combining them. I just beat it longer.
I don’t know if this will help your situation, but sometimes we overthink things, and get into trouble because of it. We do things the same way forever, and then for some reason we change it. My Grandma never even thought about developing structure in her gingerbread, but she probably did, without even knowing it.
So, double check your ingredients. Maybe compare them to a similar recipe for any drastic variations from the formula.
Did you recently transcribe the recipe? Did you make any mistakes? I type everything into the computer, and you really need to double check it. You can tell if the typo is a misspelled word, but not if 1/4 is supposed to be 1/2.
And of course, you should check to make sure that your oven is operating correctly.
Things that used to work, and now don’t are a real headache. I hope you solve your mystery soon.
Best of luck,