Line a baking sheet with parchment paper and set aside.
In a heavy-bottomed saucepan, melt butter over medium heat.
Add sugar and salt, stirring constantly until the mixture reaches 300°F (hard crack stage).
Remove from heat and stir in vanilla extract.
Pour the mixture onto the prepared baking sheet and spread evenly.
Sprinkle chocolate chips over the hot toffee and let them melt. Spread evenly.
Top with chopped nuts, if using.
Allow to cool completely, then break into pieces.