I've been looking around for a lemon filling recipe that doesn't need to be refrigerated. I like the Costco type recipe that uses whipped cream. But I'm making a cake for a couple that is transporting it to their son's house for Christmas. Will that recipe be okay on a cake that won't be in the refrigerator???
One idea you can use is that lemon goo in a sleeve (the kind best used for jelly donuts) mixed with either buttercream frosting or Rich's Bettercreme. I've done it both ways. You might want to add a little lemon juice for a richer lemon taste. I did that for the filling of some of the layers for the towering inferno cake (in my pix) and we called it "lemon creme filling" and the lady went ga-ga over that!
You can add a few drops of lemon extract or juice and rind to your normal buttercream.