Prepare the Phyllo Dough: Begin by thawing the phyllo dough as directed on the packaging, ideally overnight in the refrigerator. Before assembling, bring the dough to room temperature by leaving it on the counter for about an hour. Trim the sheets to fit your 13x9-inch baking dish. Keep the unused sheets covered with a damp towel to prevent drying out.
Butter the Baking Pan: Using melted butter, generously coat the bottom and sides of your non-stick baking dish. This step helps prevent sticking and contributes to the crispness of the final baklava.
Make the Honey-Lemon Syrup: In a medium saucepan, combine sugar, honey, lemon juice, and water. Bring the mixture to a boil over medium-high heat, stirring until the sugar dissolves completely. Then reduce the heat to medium-low and let it simmer gently without stirring for 4 minutes. Remove from heat and allow the syrup to cool while you prepare the baklava layers.
Prepare the Nut Filling: Pulse the walnuts in a food processor about 10 times or chop finely by hand until coarsely ground. Transfer to a bowl and mix in the ground cinnamon until well combined.
Layer the Phyllo and Nuts: Start by placing 10 sheets of phyllo dough into the baking dish, brushing each sheet lightly with melted butter before adding the next. Spread approximately 3/4 cup of the walnut mixture evenly over the layered phyllo. Then add 5 more buttered phyllo sheets on top. Repeat this process of layering nuts and phyllo sheets four times, finishing with a final layer of 10 buttered phyllo sheets on top. Brush the surface generously with butter.
Score the Baklava: Using a sharp knife, carefully cut the layered pastry into 1.5-inch wide strips, then slice diagonally to create diamond-shaped pieces. This scoring will help the baklava bake evenly and make serving easier.
Bake to Golden Perfection: Place the baklava in a preheated oven at 325°F (163°C) and bake for about 1 hour and 15 minutes, or until the top is golden brown and crisp.
Add the Syrup: Once removed from the oven, immediately pour the cooled honey-lemon syrup evenly over the hot baklava. The sizzling sound confirms that the syrup is soaking into the layers, keeping the pastry crisp rather than soggy.
Cool and Serve: Allow the baklava to cool completely at room temperature, uncovered. For optimal flavor and texture, let it rest for 4 to 6 hours or overnight, allowing the syrup to fully permeate the layers. Optionally, garnish with extra chopped walnuts or drizzle with melted chocolate before serving.