When you reading the food parts of the travel guides of Turkey, you're probably know what the Baklava is.
I do not want to bore you with the historical information about baklava. Baklava is prepared on large trays and cut into different shapes. It includes layers of filo filled with chopped nuts and sweetened and held together with syrup or honey.
Karakoy Gulluoglu is the best pastry that sells Baklava. So, don't forget to visit there in your Istanbul days.