This may have been covered before but I could not find a post about it or actually figure out exactly what to search on.
Anyway, I have made cakes and used various jellies like strawberry and raspberry for fillings without a problem. Today I made a cake and wanted to try filling it with a white zinfandel jelly I found. It smells and tastes yummy but it was very thin. I mixed it with some buttercream to try to give it a little more substance but I still had problems with the cake layers shifting a bit. Any ideas on how to stiffen or handle a really runny filling?
Did you make a stiff buttercream dam first? You use your icing bag with just a coupler in it and make a bead in about 1/4 inch all around the outer rim of your cake. Then go sparingly with any runny filling and make sure you fill the cake well below the icing dam height. Then place upper cake on top and press down slightly.
With the runny fillings, some folks sandwich them between two layers of buttercream. Adding extra icing sugar and less liquid is about all you can do to counter this runny filling when mixing it into your buttercream.
Hugs Squirrelly Cakes