Preheat the oven to 400°. Butter a 13-by-9-inch glass baking dish. In a food processor, pulse the pistachios with 1/2 cup of the sugar just until the nuts are finely ground. Transfer to a medium bowl and stir in half the butter.
Stack the phyllo sheets and cut them in half crosswise. Set a half sheet of phyllo in the prepared baking dish and brush lightly with some of the remaining melted butter. Repeat with 11 more half sheets of phyllo, buttering each sheet; don't worry if the pastry tears a little. Cover the remaining phyllo with a towel.
Spread the pistachio mixture evenly on the phyllo in the baking dish. Top with the remaining phyllo sheets, buttering each sheet as above. Drizzle any remaining butter over the top. Using a sharp knife, make diagonal slices 1 1/2 inches apart all the way through the baklava; slice similarly in the opposite direction to make a diamond pattern. Bake for about 20 minutes, or until evenly browned on top.
Meanwhile, in a saucepan, combine the remaining 1 cup of sugar with the water and bring to a boil over moderate heat, stirring to dissolve; remove from the heat. Stir in the honey and cinnamon. Pour the syrup evenly over the baklava and let cool completely before serving.