Preheat oven to 350°F (175°C). Line a 9x13-inch baking pan with foil and lightly grease it.

In a large saucepan, melt the butter over medium heat.

Add the sugar and salt, stirring constantly until the mixture boils.

Allow it to boil for 5 minutes without stirring, making sure to watch carefully to avoid burning.

Remove from heat and stir in vanilla extract.

Immediately pour the hot toffee mixture evenly into the prepared pan.

Sprinkle the chocolate chips evenly over the hot toffee and let them sit for 2 minutes to melt.

Using a spatula, spread the melted chocolate over the toffee evenly.

Sprinkle chopped nuts and butterscotch chips (if using) evenly over the chocolate layer, pressing them lightly to adhere.

Let the toffee cool at room temperature until completely set, then refrigerate for at least 1 hour.

Once firm, lift the toffee from the pan using the foil and break it into pieces.