**Preheat the Oven**: Preheat your oven to 350°F (175°C).
**Prepare the Pan**: Brush a 9x13 inch baking pan with some of the melted butter. Lay the first layer of phyllo dough in the pan, then brush with more melted butter. Repeat this step for about 8 sheets.
**Add the Nut Filling**: Mix the chopped walnuts with cinnamon. Sprinkle a thin, even layer of the nut mixture on top of the buttered phyllo.
**Continue Layering**: Add 2 more sheets of phyllo, buttering each sheet. Repeat until half the phyllo dough and filling is used up.
**Add More Nuts**: Layer the remaining nut mixture on top, then continue layering the rest of the phyllo dough, again buttering each sheet.
**Cut the Baklava**: Before baking, cut the layered baklava into diamond or square shapes with a sharp knife.
**Bake**: Bake for 45-55 minutes, or until the phyllo is golden brown and crisp.
**Make the Syrup**: While the baklava bakes, combine sugar, water, honey, and lemon juice in a saucepan. Bring to a boil, then reduce to a simmer for about 10 minutes. Stir occasionally and remove from heat. Add vanilla extract, if desired.
**Syrup the Baklava**: Once the baklava is done, immediately pour the hot syrup evenly over the baked layers. Let the baklava absorb the syrup and cool for at least 2 hours.
**Serve**: Cut along the pre-made lines and enjoy!