Thaw the phyllo pastry if it is frozen and required on the package. Move on to the next step of it is not.
Prepare the syrup: Combine the sugar, water, honey, cinnamon stick and lemon slice in a saucepan. Stir over medium-high heat until it starts to boil. Then, lower the heat and let it simmer for 10-15 minutes. After that, remove the lemon slice and the cinnamon stick and set it aside to cool.
Prepare the filling: Coarsely chop your selected nuts, ensuring a chunky texture rather than a fine grind. Set aside.
Prepare the oven, phyllo sheets and pan: Preheat your oven to 350°F (180°C). Trim the phyllo dough sheets to fit into your round baking pan (we use a 10-inch / 25-cm round baking pan). Cover them with a kitchen towel so that they don't dry. Then, brush the bottom and sides of your pan with some of the melted butter.
Layer the baklava: Lay one sheet of phyllo dough in the pan, and brush it with melted butter. Repeat with 5 more sheets, so you end up with 6 sheets layered and buttered. Sprinkle ¼ of your chopped nuts evenly over the buttered phyllo dough.
Continue this process, creating 4 layers of nuts and 5 layers of buttered phyllo dough. Each phyllo layer should consist of 6 sheets, and remember to sprinkle the nuts after every fifth buttered sheet.
Once your final layer of phyllo is in place, make sure to also butter the top layer. Using a sharp knife, cut the baklava into diamonds or squares before baking.
Bake: Bake the baklava for about 30 minutes, or until it is golden brown and crisp.
Pour the syrup over hot baklava: Immediately after removing the baklava from the oven, pour the cooled syrup over it slowly, ensuring it goes into the cuts. This will create a pleasing sizzle. Let it rest uncovered for 4-5 hours, allowing the flavors to fully merge together.
Garnish: When serving, you can garnish it with ground pistachio if you want.