Line two shallow oven cookie trays with non stick baking paper and set aside.
Place sugar, syrup, butter and vanilla into slow cooker.
Turn onto HIGH and stir until well combined
Cover and cook on HIGH for 1hr.
After the hour stir again, then gradually add baking soda in small portions, stirring well each time to combine, until all baking soda has been added. Stir to combine well.
Cover and cook still on HIGH for another 30mins.
Add in nuts and stir to combine, then cover and cook a further 20mins on HIGH or until a rich toffee colour is achieved.
Carefully pour half the mixture into each lined tray (use oven mitts to hold it as the cooker insert will be hot)
Even the mixture out with a spatula and let cool on bench for 1hr.
For ease of shattering, place the trays into the freezer for 10mins after the 1hr cooling period and prior to breaking.
Then cover the tray with a clean teatowel and break apart using a kitchen hammer or a heavy can etc.
Break into rough chunks as large as you like :)
Store in sealed container - in hot climate store this container in fridge (surface may go tacky to the touch in fridge)
Option: Alternatively can be poured into little patty cake cases as per photo if you rather individual toffee's :)