Line a baking sheet with parchment paper or a silicone baking mat.

In a heavy-bottomed saucepan over medium heat, combine butter, sugar, and salt. Stir constantly until it boils, then reduce heat slightly and continue stirring until the mixture reaches about 285°F (soft crack stage).

Remove from heat, stir in vanilla extract, pour hot toffee onto prepared baking sheet and spread evenly.

Sprinkle chocolate chips over hot toffee and let sit for a minute to melt.

Use a spatula to smooth melted chocolate, then sprinkle chopped nuts over the top.

Let the toffee cool completely at room temperature until hardened (about 2 hours), then break into pieces.