Put the phyllo in the refrigerator 24 hours ahead of time to defrost.
Put the pistachios and sugar in the bowl of your food processor and pulse.
After about 5 pulses, sprinkle 1 teaspoon rose water over the pistachios then continue pulsing until finely ground. Be careful with your pulsing so you don't end up with pistachio butter!
Heat oven to 325°.
Using a pastry brush, brush ghee over the surface of a rimmed sheet pan, including the sides.
Unroll your defrosted phyllo sheets on a smooth surface and have a piece of waxed paper or slightly damp towel ready to keep the unused pieces covered.
Peel off one piece of phyllo and carefully lay it flat on the bottom of the buttered pan. If it tears, it's okay, just put it back together like a puzzle.
Brush some ghee over to cover the surface. You can hold the phyllo sheet down with your fingertips to prevent it from moving.
Lay another sheet of phyllo over the first and brush with ghee. Continue with the phyllo and ghee until you have 8 sheets stacked up.
Spread half of the nut mixture over the 8 sheets of phyllo.
Lay a sheet of phyllo on top of the nuts and brush with ghee. Continue stacking the phyllo until 5 sheets are stacked.
Spread the remaining nuts over the phyllo.
Lay another sheet of phyllo on top of the nuts, brush with ghee and continue with phyllo and ghee until all the sheets are used. (There should be 5 to 6 sheets in this layer.)
Using a sharp knife cut the Baklava into diamonds or triangles.
Bake for 45 to 55 minutes until light brown.
While the pastry is baking make the Sugar Syrup.