1. Preheat oven to 325°.
2. In a blender or food processor, whirl 1/2 cup sugar with the almonds and walnuts just until finely ground (don't overprocess or mixture may turn into nut butter). Pour into a bowl and stir in remaining 1/2 cup sugar and the cinnamon.
3. Unroll filo dough and cover with plastic wrap. Keep filo covered as you work so it doesn't dry out.
4. Brush bottom and sides of a 9- by 13-inch baking pan with melted butter. Line pan with 1 sheet of filo (it can extend over pan sides). One at a time, layer 7 more sheets over the first, gathering each to fit into pan and lightly brushing each with butter.
5. Sprinkle a fourth of the nut mixture over buttered filo in pan. Lay another sheet of filo on top, gathering it to fit into pan and brushing with butter. Repeat layering of nut mixture with filo sheets and butter until all nut mixture is used.
6. Layer all but one of the remaining filo sheets on top, gathering each to fit pan and brushing with butter. Lay the last sheet flat on top and brush with butter. Trim to fit pan.
7. With a sharp knife, cut a 2-inch diamond pattern about 1/4 inch deep. If desired, cut a small hole in the center of each diamond and insert a clove to anchor layers. Bake until top is golden and crisp and edges pull away from pan sides, 45 to 55 minutes. Set pan on a rack.
8. Slice along cuts, almost (but not completely) to bottom. Pour spiced syrup over baklava. Let stand to absorb most of the syrup, at least 3 hours. Cut through bottom layer and serve.
Spiced syrup: In a medium pan, mix 2 cups sugar, 1 cup water, 3 tablespoons honey, 2 tablespoons lemon juice, and 1 cinnamon stick (about 3 in. long). Cook, uncovered, over medium heat, stirring occasionally, until mixture is reduced to about 1 3/4 cups and has the texture of light syrup, 15 to 20 minutes. Let cool to lukewarm, stirring occasionally, 15 to 25 minutes. Discard cinnamon stick.
Note: Nutritional analysis is per piece.