Bring the ingredients to a boil in a small saucepan and continue to boil for about 15 minutes, until the syrup is thick and has reached a temperature of about 230 ºF (110 °C). Transfer to a container and cool completely (can be made the day before and stored on the counter, or chill it in the fridge for a few hours to speed up the process).
For the filling
Peeling the pistachios is optional, but whether you do or you don't, grind the pistachios with 2 tablespoon sugar in the food processor by pulsing, until the mixture forms a medium-fine grind.
Set aside
To make the baklava
Preheat the oven to 325ºF (165 °C). Be sure there is a rack in the middle of the oven, and one above.
Butter a 9x13 Pyrex glass dish (find it on Amazon).
Prepare the phyllo dough by unwrapping it and unrolling it. Cut the stack in half, width-wise so that you have two stacks of ~9x13" sheets. Set them aside, being sure to keep them covered with a slightly damp kitchen towel to prevent the sheets from drying and becoming brittle and flakey.
Begin layering the phyllo by placing 2 sheets in the bottom of the prepared pan, then brushing them with melted butter. Repeat this until you've used up half the package of phyllo, ending with melted butter.
Sprinkle the ground nut filling over top, then 2 tablespoon melted butter, and press everything down evenly in the pan.
Continue layering the phyllo on top, this time buttering every single sheet as you go.
End with butter.
Cut the baklava into squares, diamonds, or a more elaborate pattern. Drizzle the leftover melted butter over top, letting it run down in the cuts and grooves (if you've got more than a few tablespoons, drizzle a couple over top and store the leftovers in the fridge). Sprinkle water over top.
Bake the baklava for 30 minutes on the middle rack, then move it up and bake for another 30 minutes, until the top is nice and golden.
Remove the baklava from the oven and immediately pour over all of the syrup. The syrup will sizzle as it hits the hot pan.
Let the baklava cool completely, then recut it before serving.
Notes
When my mom would make baklava, she would go through the step of clarifying the butter to remove the milk solids. This will allow you to store the baklava for longer without the risk of the butter going rancid. It also leads to a cleaner flavour. I'm lazy, so I use straight melted butter.
This is a recipe for Egyptian baklava made with pistachios. If you want to use rose water or orange blossom water, remember to use them sparingly. Too much rose water will make the dessert bitter.
Note that the Greeks make the syrup for baklava with honey.