1. Preheat the oven to 175C.
2. Combine the first 3 ingredients in a medium saucepan over low heat; stir until the golden syrup dissolves. Increase heat to medium and cook for a further 8 minutes. Remove from heat; keep warm. Discard cinnamon stick.
3. Microwave the hazelnut-chocolate spread for 30 seconds. Combine with the hazelnuts, pistachios, almonds, walnuts, ground cinnamon and salt.
4. Lightly coat a 13 x 9-inch baking dish with oil.
5. Place 1 phyllo sheet lengthwise in the bottom of the prepared pan, allowing the ends of the sheet to extend over the edges of the dish; lightly brush with butter.
6. Repeat the procedure with 5 phyllo sheets and butter. Drizzle 1/3 cup melted hazelnut -chocolate spread over the phyllo and then sprinkle one-third of the nut mixture on top.
7. Repeat the procedure twice with phyllo, butter, hazelnut-chocolate spread, and nut mixture.
8. Top the last layer of nut mixture with the remaining 6 sheets of phyllo, each lightly brushed with butter. Press gently into the pan.
9. Cut lengthwise 3 times and crosswise 5 times cuts to form 24 portions using a sharp knife.
10. Bake for 35 minutes until golden.
11. Drizzle any remaining syrup mixture over the baklava, allow to cool on a wire rack, and enjoy!