Preheat your oven to 325˚F.
Place the walnuts in a food processor and pulse about 10 times until they are coarsely ground or finely chopped. In a medium bowl, mix together the chopped walnuts and 1 teaspoon of ground cinnamon.
In your prepared baking pan, lay down 10 phyllo sheets, one at a time, brushing each sheet with melted butter after placing it in the pan. Continue by layering another phyllo sheet, brushing with butter, and so on. Always keep the remaining phyllo sheets covered with a damp towel to prevent them from drying out. Once you have layered the 10 sheets, evenly spread about 3/4 cup of the nut mixture over the phyllo.
Next, add 5 more buttered phyllo sheets, followed by another layer of the nut mixture. Repeat this process four more times. For the final layer, place 10 buttered phyllo sheets on top, and brush the very top layer generously with butter.
Using a sharp knife, cut the pastry into strips that are 1 1/2 inches wide. Then, cut diagonally to form diamond shapes. Place the baking pan in the oven and bake at 325˚F for 1 hour and 15 minutes, or until the tops are golden brown.
Upon removing the baklava from the oven, immediately pour the cooled syrup evenly over the hot pastry. You’ll hear a sizzle, which ensures that the baklava remains crisp rather than becoming soggy. Allow the baklava to cool completely, uncovered, at room temperature. For the best flavor and texture, let it rest for 4-6 hours or overnight, giving the syrup time to fully penetrate and soften the layers. Garnish with finely chopped nuts or a drizzle of melted chocolate if desired. Store at room temperature, covered with a tea towel, for 1 to 2 weeks.