Line a jelly roll pan with parchment paper.

Melt butter in a saucepan over medium heat.

Stir sugar and salt with melted butter to dissolve completely.

Remove saucepan from heat, add peanuts, and stir to coat completely; immediately pour onto the prepared pan and spread into an even layer.

Refrigerate until brittle, at least 30 minutes.

Separate from parchment and break into pieces.