Prep phyllo dough: Thaw phyllo dough by package instructions (overnight in fridge, then 1 hour at room temperature). Trim sheets to fit your 13x9 inch baking pan. Keep unused sheets covered with damp towel.

Prepare baking pan: Butter the bottom and sides of a 13x9 inch non-stick baking pan thoroughly.

Make honey syrup: In medium saucepan, combine sugar, honey, lemon juice, and water. Bring to boil over medium-high heat, stirring until sugar dissolves. Reduce heat to medium-low and boil 4 minutes without stirring. Remove from heat and let cool completely.

Prepare nut filling: Preheat oven to 325°F. Pulse walnuts 10 times in food processor until coarsely chopped. Mix with cinnamon in medium bowl.

Start layering: Place 10 phyllo sheets in baking pan one at a time, brushing each sheet with melted butter before adding the next. Keep remaining phyllo covered with damp towel.

Add nut layers: Spread 3/4 cup nut mixture over phyllo. Add 5 buttered phyllo sheets, then another 3/4 cup nuts. Repeat this pattern 4 times total.

Finish layers: Top with final 10 buttered phyllo sheets. Brush the very top with butter.

Cut and bake: Cut pastry into 1 1/2 inch wide strips, then cut diagonally to form diamond shapes. Bake at 325°F for 1 hour 15 minutes until tops are golden brown.

Apply syrup: Remove from oven and immediately spoon cooled syrup evenly over hot baklava (you'll hear it sizzle). Let cool completely uncovered at room temperature.

Rest and serve: For best results, let baklava sit 4-6 hours or overnight at room temperature for syrup to penetrate layers. Garnish with chopped nuts or melted chocolate if desired.