I love this cake, it is one of my favorite recipes. We always include fruit in the middle, usually apples but sometimes peaches. (That blueberry one sounds lovely, too!)
It shouldn’t turn out dry, even without the fruit. It seems like a common problem with dry buttercakes is overbaking (too long/hot or pan too large; reduce temp by 25 if using convection fan).
Other possible problems that could make this recipe dry include not using all yolks, using too little sugar or butter, using too much flour (did you weigh the flour and sugar?) or not using real sour cream.
Hope that helps!