Toast chopped macadamia nuts in a dry skillet over medium heat until lightly golden and fragrant, approx. 5 min. Mix in pistachios. Set aside. Generously grease a rimmed baking sheet with butter or vegetable oil. Set aside.
In a medium-size heavy saucepan, combine sugar, corn syrup and 1/4 cup (60 mL) water over medium heat. Stir occasionally until dissolved, then cook without stirring, brushing down the sides of saucepan with a pastry brush dipped in cold water (to prevent bits of sugar from hardening on the pan’s sides). Cook 10 min. until “soft ball” stage or a candy thermometer reads 234°F (112°C).
Stir butter into sugar mixture and cook 10 to 15 min. longer, until “hard crack” stage or a candy thermometer reads 300°F (150°C). Remove from heat.
Working quickly, use a heatproof spatula to stir in vanilla, nuts and baking soda and pour onto prepared baking sheet, spreading evenly. Sprinkle with salt. Cool completely before breaking into pieces.