Preheat your oven to 350 F degrees. Lightly spray a baking sheet with cooking spray. If you use a 13x9 baking dish, the phyllo sheets will be bigger, so you might need to cut the ends off, either before using them, or after you've done layering the baklava, or you can simply tuck the ends in.
If your nuts aren't toasted, simply place them on a baking sheet in a single layer and roast them for a few minutes in the oven, just until you start smelling them. Make sure you don't forget them as they will burn quickly.
Place all the nuts in a food processor and pulse a few times until they are finely chopped.
Combine all the nuts with the ground cinnamon and salt in a bowl and set aside.
Microwave the Nutella for about 30 seconds on high, until melted and easily spreadable.
Take one phyllo sheet and lay it on the bottom of the baking sheet. While working with one phyllo at a time, make sure you cover the other sheets with a damp towel. Brush this phyllo sheet evenly with butter. Repeat with 5 more sheets, you should end up with 6 sheets, all brushed with butter. Drizzle about 1/3 cup of the melted Nutella and spread with a spatula as evenly as you can. Sprinkle evenly with 1/3 of the nut mixture.
Repeat the above step with 6 more phyllo sheets, Nutella and nut mixture, two more times, ending with 6 sheets of phyllo. Therefore you'll have 3 layers of Nutella and nuts and 4 layers of buttered phyllo sheets. Press gently into pan. Cut the ends off if necessary, or simply tuck them in.
Cut into equal size squares or diamond shapes, using a very sharp knife.. You should end up with about 24 pieces.
Bake for 35 minutes or until phyllo is golden brown and the edges appear slightly crisp.
While the baklava is baking, make the syrup by adding all the syrup ingredients in a small saucepan and bringing it to a boil over medium heat. Turn the heat down and let it simmer for about 5 to 7 minutes. Remove from heat and keep warm.
After you remove the baklava from the oven, immediately drizzle the honey mixture over the baklava. Cool the baklava in the pan.