Preheat the oven to 350°F.
Take out the phyllo sheets and cover them with a damp towel to keep them from drying out.
Brush the bottom of a 9x13 tray with melted butter. Add a phyllo sheet, letting the sides hang over the edges of the pan.
Brush the phyllo sheet with butter and add another sheet on top. Repeat until you have 9 to 10 sheets stacked.
Pour the custard on top of the phyllo sheets, then repeat the butter and phyllo layering until you have another 9 to 10 layers.
Cut the assembled pie into 12 equal pieces with a sharp knife.
Bake for 45 to 50 minutes until the top is golden and crispy.
Remove from the oven and immediately pour the simple syrup over the top. Use as much or as little as you like.
Garnish with chopped pistachios and rose petals.
Let the syrup soak in for at least an hour before enjoying!