Preheat the oven to 350F (180C), and grease a 9x13-inch brownie pan with the melted butter.
Layer five sheets of phyllo, brushing each with the melted butter using a pastry brus.
Sprinkle 1/4 of the nut mixture (about 1 1/2 cups, 200g) into an even layer.
Repeat with another layer of dough made of five sheets, each brushed with butter.
Sprinkle with another layer of nuts.
Repeat with the rest of the dough and nuts mixture. You should have a total of 5 layer of phyllo, and four layers of nuts.
Use a very sharp knife to mark the cake from in 3-4 vertical lines.
Now use the knife to make marks diagonally to the vertical lines.
Bake for 30 minutes, than reduce the temperature to 300F (150C) and bake for another 30 minutes.
Make the syrup as the baklava bakes