Combine syrup ingredients in a small saucepan and bring to a full boil over medium-high heat, occasionally stirring to ensure that sugar dissolves. Transfer to 2-cup measuring cup and set aside to cool while making and baking baklava; when syrup is cool, discard spices and lemon zest. (Cooled syrup can be refrigerated in an airtight container for up to 4 days.)
MAKE THE NUT FILLING:
Pulse almonds in a food processor until very finely chopped, about twenty 1-second pulses; transfer to a medium bowl. Pulse walnuts in a food processor until very finely chopped, about fifteen 1-second pulses; transfer to bowl with almonds and toss to combine. Measure out 1 tablespoon nuts and set aside for garnish. Add cinnamon, cloves, sugar, and salt; toss well to combine.
ASSEMBLE:
Brush 13 x 9-inch traditional (not nonstick) baking pan with butter. Adjust oven rack to lower-middle position and heat oven to 300 degrees. Unwrap and unfold phyllo on a large cutting board; carefully smooth with hands to flatten. Using the baking pan as a guide, cut sheets crosswise with a chef’s knife, yielding two roughly evenly sized stacks of phyllo (one may be narrower than the other). Cover with plastic wrap, then damp kitchen towel to prevent drying.
Place one phyllo sheet (from the wider stack) at the bottom of baking pan and brush until completely coated with butter. Repeat with 7 more phyllo sheets (from the wider stack), brushing each with butter.
Evenly distribute about 1 cup of nuts over phyllo. Cover nuts with a phyllo sheet (from the narrower stack) and dab with melted butter (phyllo will slip if butter is brushed on). Repeat with 5 more phyllo sheets (from the narrower stack), staggering sheets slightly if necessary to cover nuts, and brushing each with butter. Repeat layering with additional 1 cup nuts, 6 sheets phyllo, and the remaining 1 cup nuts. Finish with 8 to 10 sheets phyllo (from the wider stack), using nicest and most intact sheets for uppermost layers and brushing each except final sheet with butter.
Use palms of hands to compress layers, working from the center outward to press out any air pockets. Spoon 4 tablespoons of melted butter on the top layer and brush to cover all surfaces. Use a bread knife or any other serrated knife with a pointed tip in a gentle sawing motion to cut the baklava into diamonds, rotating the pan as necessary to complete the cuts. (Cut on the bias into eighths on both diagonals.)
BAKE AND FINISH:
Bake until golden and crisp, about 1.5 hours, rotating the baking pan halfway through baking. The top should be golden brown. Immediately after removing the baklava from the oven, pour cooled syrup over cut lines until about 2 tablespoons remain (syrup will sizzle when it hits the hot pan); drizzle remaining syrup over the surface. Garnish the center of each piece with a pinch of reserved ground nuts. Cool to room temperature on a wire rack, about 3 hours, then cover with foil and let stand at least 8 hours before serving. (Once cooled, baklava can be served, but flavor and texture improve if left to stand at least 8 hours. Baklava can be wrapped tightly in foil and kept at room temperature for up to 10 days.)
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Notes
Depending on your cuts, this recipe will make about 32-40 diamond-shaped pieces.
A straight-sided traditional metal baking pan works best for making baklava; the straight sides give the Baklava nicely shaped edges.
Make sure that the phyllo is fully thawed before use; leave it in the refrigerator overnight or on the countertop for four to five hours. When assembling, use the nicest, most intact phyllo sheets for the bottom and top layers; use sheets with tears or ones that are smaller than the size of the pan in the middle layers, where their imperfections will go unnoticed.