Preheat oven to 170°C / 338°F using the oven's upper and lower heat function.
Lay open the phyllo stack on your working surface and cover it with a tea towel (so it won't air-dry).
With a pastry brush, brush an 11''x15''/ 26x36 cm baking pan with melted butter.
NOTE: To create the base of the Baklava you will need 4 phyllo sheets. 2 to cover the pan lengthwise, and 2 to cover the pan widthwise. Each phyllo sheet should hang out of the pan a bit, in order to overlap it on top later on.
Add the 4 phyllo's for the base in the pan as explained above and brush each one with butter.
Sprinkle with 2-3 handfuls of the nut filling on top.
Add next phyllo and fold all four sides inwards. Brush with butter.
Add another phyllo and fold it exactly the same way. Grease with butter and add 2-3 more handfuls of filling.
Repeat the process 2 more times.
Add the last 2 phyllo sheets on top (if your stack had a few more phyllo's simply add them on top as well always brushed with butter).
Overlap the excess phyllo (that hangs out of the pan) on top. Brush with the remaining butter.
Cut the Baklava (all the way through to the bottom) into triangular pieces.
Place the pan on the oven's lowest rack. Bake for about 1h and 20 minutes. Or until Baklava is deeply golden on top and very crispy.
Once the Baklava is baked, ladle the cold syrup on top.
Let Baklava reach room temperature before refrigerating.
Refrigerate for at least 3-4 hours before serving.
Serve with some extra honey or nuts on top.