Preheat your oven to 325 degrees. Melt your butter and have a kitchen brush on hand.
Butter the bottom of your pan and lay phyllo sheets on the bottom of the pan making sure they have an overhang on both the left and right side, as well as the top and bottom.
Everytime you lay down a piece of phyllo, generously butter the phyllo sheet. Work quickly because the phyllo can dry out. If you are worried about being too slow, I suggest covering the phyllo you are not working with with a damp towel as you work.
After you have evenly lay your phyllo sheets in your pan, with butter between each layer and overhang around your pan, pour in your custard.
Smooth the top if necessary and not you may either choose to cut some excess phyllo layer before folding (for a thinner phyllo top layer) OR you may layer each of the overhang layers over each other, remembering again to butter between each layer.
When your custard is fully covered with phyllo, pour the remaining butter on the top layer of phyllo , sprinkle with a bit of water, and score the top of the custard covered phyllo with markings of how you think you will cut the final custard. Making sure you reach the custard layer so steam can be released.
Bake in your oven for 75 minutes, until the top is nicely browned.
Remove from the oven and immediately pour your cooled syrup all over. It may be puddy when it comes out of the oven but this goes down when it cools and steam escapes. .
Let it sit at room temp while the syrup is soaking until it cools. Serve after the syrup has soaked in or place in the fridge and serve cold.
Tip: It is very easy to cut when it is cold but I like the way it tastes at room temp best so I prefer to refrigerate the custard, cut clean slices and keep my slices at room temp before enjoying with icecream and a bit of crushed pistachio.