Place balsamic vinegar in a saucepan and bring to a boil.
Reduce heat so it stays at a strong simmer until reduced by one-third
Dip a spoon, and when the mixture coats a spoon, it is done.
Remove it from heat and allow the balsamic reduction to cool
It will thicken as it cools, if it gets too thick, then add more vinegar and return it to the heat and stir. If it is too thick, repeat until it reaches the consistency you would like.
Cool balsamic
Layer mozzarella slices, with strawberries, sprinkle blueberries over the top, and drizzle with balsamic!