Thaw the phyllo dough according to package instructions, and prepare the simple syrup ahead of time so it's at room temperature.
Coarsely chop the walnuts in the food processor and transfer them to a bowl.
Add the sugar, cinnamon, rose water, and orange blossom water.
Mix well and set aside.
Melt the ghee and butter in a bowl and set aside.
Count the phyllo dough sheets in the package. We are looking for 30-34 sheets. The Athens brand has two divided wrapped phyllo dough sheets per 1 pound package, which makes it easy to use.
Brush 1 tablespoon of butter/ ghee onto your 9*13 pan. Trim about ½ inch to ¾ inch of phyllo dough from the short side to make it fit the pan. You can also use a slightly bigger pan without trimming.
Place 3 sheets of phyllo at a time, flat, then lightly brush with the ghee and butter mixture. Repeat until half the amount of sheets are finished.
Place the walnut mixture evenly.
Now, lay another 2 phyllo sheets on top and lightly brush with butter/ ghee mixture. Place another 3 sheets and repeat. For the last sheet, lightly brush.
You should have some ghee/ butter leftover, about ½ cup.
Cut the baklawa into your desired shape, making sure to cut all the way to the bottom.
Pour the remaining amount of butter/ ghee all over, so it gets through the cuts.
Place in the oven at 350 F for about 50-55 minutes, until it gets golden. You can rotate the pan half way to make sure it browns evenly. Once out of the oven, immediately pour the room temperature syrup on top.
Garnish with finely chopped pistachios (if desired) and place into the fridge to cool for 2-3 hours.
Once cooled, reinforce the cuts again. Let it come to room temperature before removing and serving. Do not cover.