To make the syrup: Stir the sugar, water, lemon juice, and if using, the corn syrup, cinnamon sticks, and/or cloves over low heat until the sugar dissolves, about 5 minutes. Stop stirring, increase the heat to medium, and cook until the mixture is slightly syrupy, about 5 minutes (it will register 225 degrees on a candy thermometer). Discard the cinnamon sticks and whole cloves. Let cool.
To make the filling: Combine all the filling ingredients.
Preheat the oven to 350 degrees. Grease a 12-by-9-inch or 13-by-9-inch baking pan or 15-by-10-inch jelly roll pan.
Place a sheet of phyllo in the prepared pan and lightly brush with butter. Repeat with 7 more sheets. Spread with half of the filling. Top with 8 more sheets, brushing each with butter. Use any torn sheets in the middle layer. Spread with the remaining nut mixture and end with a top layer of 8 sheets, continuing to brush each with butter. Trim any overhanging edges.
Using a sharp knife, cut 6 equal lengthwise strips (about 1 3/4 inches wide) through the top layer of pastry. Make 1 1/2-inch-wide diagonal cuts across the strips to form diamond shapes.
Just before baking, lightly sprinkle the top of the pastry with cold water. This inhibits the pastry from curling. Bake for 20 minutes. Reduce the heat to 300 degrees and bake until golden brown, about 15 additional minutes.
Cut through the scored lines. Drizzle the cooled syrup slowly over the hot baklava and let cool for at least 4 hours. Cover and store at room temperature for up to 1 week. If the baklava dries out while being stored, drizzle with a little additional hot syrup.