Lightly spray a 9x13 inch baking dish with butter flavored cooking spray. Arrange chopped cashews in the bottom of dish.
Combine brown sugar, golden syrup, sweetened condensed milk, and butter in a large, heavy bottomed saucepan. Bring to a boil over medium-high heat. Do not stir once the sugar syrup begins to boil. Heat to 250 degrees F (120 degrees C), or until a small amount of syrup dropped into cold water forms a rigid ball.
Pour caramel over top of cashews. Stir well. Use a heatproof rubber spatula to spread the mixture evenly in the dish; allow to cool for 1 hour. Cut cooled caramel into squares or roll into balls as desired.