In a food processor, pulse the pistachios in 2 second intervals until coarsely ground.
In a small pot over medium heat, melt the butter and allow to cook until a white foam forms atop and the milk solids fall to the bottom of the pot. Gently remove the milk foam from the top and slowly pour the rest of the unmelted butter into a small bowl. Be careful to leave behind the milk solids that have accumulated at the bottom of the pot.
Brush the inside of an 8x8 pan with some of the clarified butter. Set aside.
Cut the phyllo sheets in half and cover with a lightly damp towel.
To assemble the baklava, place 1 piece of phyllo on the bottom of the baking pan, then brush with clarified butter. Place another piece of phyllo atop and continue the process until halfway up the pan.
Leaving 2 tbsp of pistachios behind, spread the pistachios into an even layer then continue layering the baklava with the remaining phyllo and clarified butter.
Once fully layered, cut the baklava into 24 pieces. Brush top with clarified butter and remaining pistachio, then place into the oven and bake until golden brown, approximately 45 minutes to an hour.
While the baklava is cooking, prepare the syrup by combining the sugar and water in a small pot and bring to a boil. Allow to cook for 10 minutes and then add the rosewater as well as the lemon juice and zest. Remove from heat and allow to cool.
Once the baklava is cooked, reheat the syrup and pour atop the baklava. Allow to cool to room temperature and serve.
