Place the butter in a saucepan and melt it over low heat until fully liquid.

Add the brown sugar and stir continuously until the mixture is smooth and well combined.

Increase the heat to medium and let the mixture gently boil, stirring constantly, until it thickens and darkens slightly.

Stir in the salt and mix evenly.

Pour the hot toffee onto a parchment-lined surface, spreading it into small bite-sized shapes.

Allow it to cool completely until hard, then break into toffee bites.