It all starts with a balsamic reduction. I used probably 1/2-1 cup of balsamic and reduced it down to this spectacular syrup.
I caramelized some onions and Brussel's sprouts and placed them atop thinly sliced potatoes. All toppings got covered in mozzarella cheese.
Give that whole pie a healthy splattering of balsamic reduction when it's all done cooking.