Wash and dry the apples, then push the wooden lolly sticks (popsicle sticks) halfway into the apples next to the stalk. Dissolve the sugar and water in a thick-bottomed pan over a gentle heat, then add the butter and syrup to the mixture and bring to the boil. Continue to boil, without stirring, until the toffee reaches 290ºC (use a sugar thermometer to measure this).
Remove the pan from the heat and gently stir in the nuts. Carefully dip each apple into the toffee, making sure each apple is well coated, then set aside to harden on a baking try lined with non-stick parchment.