Preheat the oven to 350 degrees F.
Place the butter in a medium saucepan and melt. Heat over low medium-low heat until the water and solids begin to separate, Skim off the foamy solids to clarify the butter. Pour the clarified butter into a bowl, leaving behind any solids in the pan. Set aside.
Roughly chop the pecans, almonds and pistachios in a food processor until you have a course meal. Remove the nuts from the food processor to a bowl.
To the chopped nuts add the brown sugar, ground cinnamon and cardamom. Stir to incorporate.
Lay out one sheet of phyllo dough vertically and brush with melted butter. Fold the bottom up 3 inches, then brush with butter.
Add 2 tablespoons of the nut mixture to the folded phyllo. Fold in the sides of the phyllo dough and brush with butter.
Roll the phyllo dough up from the bottom sealing in the nuts and rolling over the nuts until you have a rolled log. Place on a baking sheet. Repeat until you have 10 baklava logs.
Brush the rolled baklava tops with melted butter. Refrigerate the logs on the baking sheet for 5-10 minutes until the butter has hardened. This makes it easier to cut the baklava.
Using a serrated knife, slice the baklava logs into individual pieces. Start in the center, then slice each log into 4 even pieces about 3" long.
Bake the baklava for 30 to 35 minutes until golden brown on top.
Remove the cooked baklava from the oven and immediately pour the cold syrup over the hot baklava. It will appear to pool in the pan, but it will be soaked up by the baklava within a few hours or even overnight.
Top with chopped pistachios as garnish if desired.