Ah, yes....pastries: my weakness. But in the case of shortbread, it doesn't need the frosting to be deliciously complete. It's deceptively simple: flour, butter, sugar. The magic comes from the ratio of these 3 ingredients, as well as product quality and technique. I used to routinely make shortbread - in round cookie form - for afternoon tea in one of my restaurants, and it was always a crowd pleaser. To my palate, adding frosting to shortbread makes it a bit too sweet, not permitting the unique shortbread flavor to shine through the way it was originally meant to. On the other hand, shortbread is a good enough base for the caramel and chocolate, so why not (other flavors can be added to the dough, such as vanilla, lemon, cardamom, and on and on)? Some pastry hounds are content with the basic shortbread experience, some prefer a little "dressing up."