Line a large baking sheet with parchment paper.
Add the sugar to a large saucepan or skillet over medium heat. Let the sugar melt, stirring occasionally with a wooden spoon. Continue doing this until it turns into caramel syrup.
Once the sugar has completely melted, add the butter and mix until fully incorporated. Stir through the peanuts.
Transfer the peanut brittle mixture onto the lined sheet and spread out using a rubber spatula.
Refrigerate it for at least an hour to firm up. Once firm, break it apart into bite sized pieces.
