1. Combine 175g chocolate morsels, muscovado sugar, butter, golden syrup and salt in a heavy saucepan. Cook over medium heat, stirring constantly, until mixture come to a boil. Remove from heat. Stir in vanilla and baking soda.
2. The popcorn can also be popped on the hob, using light oil and no salt. If you use this method, weigh 7 ounces after it is popped.
3. Distribute popcorn and nuts evenly into 2 lightly greased roasting pans. Be sure to remove all unpopped kernels of popcorn before incorporating the chocolate.
4. Pour chocolate mixture evenly over popcorn and nuts, stirring well with a lightly greased spatula. Alternatively, you can use latex gloves for this step, using your hands instead of a spatula.
5. Bake at 130° (250° F) for 1 hour, stirring every 15 minutes or so. Spread on wax paper to cool, breaking apart large clumps as mixture cools.
6. Sprinkle remaining chocolate morsels evenly over hot popcorn. Let cool.