Upside down Lemon Bars, Why?
I have been making lemon bars for a while and have never had any problems. My Last 2 batches in the last week have both come out with the filling on the bottom of the shortbread base leaving me with upside down lemon bars. I was wondering why has this happened and 2x back to back. I have not changed recipes and I am not doing anything differently. My shortbread base is cooled, overly cool maybe as both times I let them sit for over the normal 15 minutes, could there be a magic window for when the filling needs to be added?
My ONLY thought is that there's a hole in the shortbread crust or it's not sealed well enough to the baking dish, so as it bakes and gets lighter (er... leavens itself? The leavening is activated by the baking? Whatever) it floats up through the not-quite-solidified filling. This happened to my pecan pies a few times and a cracked, holey, or pulled-away crust was to blame.
I think the reason for the upside down lemon bars was I may have forgot to put the flour in the lemon juice mix for both batches to thicken the quick curd. The flavor of the flourless upside down lemon bars was excellent and vibrant which now has me wondering if anyone has a lemon bar recipe that does not use flour to thicken the lemon part?
My favorite lemon bars are the Cooks Illustrated recipe. It does use a small amount of flour to thicken the filling, but it also calls for pouring the filling on without cooling the crust. I've never had a a problem with it. I like to drizzle them with white chocolate rather than dust with powdered sugar. Here's a link to a site with the recipe:
the reason why the crust rises to the surface is because the filling found its way through cracks to the bottom. Make sure when you're pushing the crust down into the pan that you got all the nooks and cranies.
I always pour the filling on top of HOT crust (take crust out of the oven, and pour filling immediately on top) which causes the layer that's in contact with the crust to cook immediately, and it prevents the upside down bars.
I also turn the temperature down from 325 to 300 after i add the filling.
PS - i just realized this thread is 2 years old. Ahh well! Hope you get something out of it anyway.
~C <-- professional baker/pastry chef