Start by lining a baking sheet with parchment paper to prevent sticking.
In a heavy-bottomed saucepan, combine the granulated sugar, water, and light corn syrup. Stir gently until the sugar is dissolved.
Place the saucepan over medium heat and attach your candy thermometer. Allow the mixture to boil without stirring until it reaches 300°F (hard crack stage).
Once the temperature is reached, remove the saucepan from heat. Quickly stir in the chopped macadamia nuts and butter until fully incorporated.
Carefully add the baking soda to the mixture. Be cautious, as it will bubble up. Stir until completely mixed.
Pour the hot mixture onto the prepared baking sheet and use a rubber spatula to spread it evenly to your desired thickness.
Allow the brittle to cool completely at room temperature, about 30-45 minutes. Once set, break it into pieces.
