Preheat the oven to 350°F (175°C). Melt the unsalted butter and lightly grease the baking dish.

Pulse the pistachios and walnuts into a coarse crumb. Transfer the chopped nuts to a mixing bowl.

Add 1/2 cup (100 g) granulated sugar and the ground cinnamon to the nuts. Stir until the filling is evenly coated.

Lay 8 sheets of filo dough in the buttered baking dish. Brush each sheet generously with melted unsalted butter.

Spread half of the nut filling evenly over the phyllo layers. Cover it with 6 buttered phyllo sheets.

Spread the remaining nut filling over the pastry. Layer the remaining filo dough on top, brushing every sheet with butter.

Cut the assembled pastry into diamond or square portions with the chef's knife. Brush the surface with the remaining melted butter.

Bake the baklava at 350°F (175°C) for 45 to 50 minutes. Remove it when the phyllo is deeply golden and crisp.

Combine the remaining 1 cup (200 g) granulated sugar, honey, water, and lemon juice in a saucepan. Simmer for 8 to 10 minutes until lightly syrupy.

Pour the warm lemon honey syrup evenly over the hot baked baklava. Let it rest at room temperature for at least 4 hours before serving.