Thaw the phyllo dough by package instructions. (This is best done by placing it in the fridge overnight then placing it on the counter for 1 hour before starting your recipe to bring it to room temperature.)
Trim the phyllo dough to fit your baking dish then cover it with a damp towel to keep it from drying out while you're working on the rest of the recipe.
Butter the bottom and sides of a 9x13 baking pan.
Honey Sauce:
(Start with this so it can cool as the Baklava bakes.)In a medium saucepan, combine the sugar, lemon juice, water, and honey.
Bring to a boil over med/high heat, stirring until the sugar is dissolved, then reduce heat to med/low and boil an additional 4 minutes without stirring.
Remove from heat and allow the syrup to cool while preparing the baklava.
Baklava Assembly:
Preheat the oven to 325°.
Pulse the walnuts 10 times in a food processor (until coarsely ground/finely chopped).
In a medium bowl, stir together 4 cups of finely chopped walnuts and 1 tsp cinnamon.
Place 1 phyllo sheet into the pan, brush the top with melted butter, place the next phyllo sheet in the pan, butter the top, etc. (Keep the remaining phyllo covered with a damp towel at all times.)
Order of the Baklava layers:
1. 10 buttered phyllo sheets2. [3/4 cup nut mixture then 5 buttered phyllo sheets]3. [3/4 cup nut mixture then 5 buttered phyllo sheets]4. [3/4 cup nut mixture then 5 buttered phyllo sheets]5. [3/4 cup nut mixture then 5 buttered phyllo sheets]6. 3/4 cup nut mixture7. 10 buttered phyllo sheets8. Butter the top
Finishing & Baking:
Cut the pastry into 1 1/2" wide strips, then cut diagonally to form diamond shapes (see photo).
Bake for 1 hour and 15 minutes or until the tops are golden brown.
Remove from the oven and immediately spoon the cooled syrup evenly over the hot baklava (you'll hear it sizzle). *This will ensure that it stays crisp instead of getting soggy.
Let the baklava cool completely, uncovered and at room temperature. For best results, let the baklava rest 4-6 hours or overnight at room temperature for the syrup to penetrate and soften the layers.
Garnish the baklava with finely chopped nuts or drizzle with melted chocolate.
Notes:
Make Ahead: This is best made ahead of time so the flavors can meld and become enhanced. Just store at room temperature, covered with a tea towel, for up to 1 week.