Chop walnuts until fine, add cinnamon and set aside.
Butter a 9×13 baking dish.
Unwrap fillo leaves and place on work surface with wax paper and a dry towel covering them to keep them from drying while working.
Stack 8 sheets of fillo in the bottom of the pan, brushing each sheet with melted butter , before adding the next one on top.
Sprinkle with a third of the nut mixture.
Top with 2 more sheets of buttered fillo, sprinkle with half of the remaining nuts.
Add two more sheets of fillo and the last of the nuts .
Top with remaining 4 sheets of filo, buttering each one.
Using a tip of a sharp knife tuck in the edges. Sprinkle lightly with water to prevent from curling.
Pre-heat oven to 325 degrees.
Using a very sharp knife, cut into diagonal parallel strips about 1 1/2 inch apart. Making about 40 pieces. Be sure to cut all the way through the bottom layer.
Bake for 1 hour or until golden brown.