Gather all ingredients: chopped nuts, butter, sugar, water, salt, vanilla, and chocolate chips. Line a 9x9 inch baking dish with parchment paper, covering the edges. Spread 1 cup of nuts on the bottom.

In a medium pot, combine butter, sugar, water, and salt. Heat over medium, stirring until melted and bubbling.

Attach a thermometer to the pot and stir until reaching hard crack stage (300°F). This takes about 10-15 minutes.

Remove from heat at 300°F, stir in vanilla, then pour hot toffee over the nuts, spreading evenly.

Let cool for about 2 minutes to set slightly before adding chocolate.

Sprinkle chocolate chips over warm toffee and cover lightly with a kitchen towel for 4 minutes to melt.

Swirl melted chocolate into the toffee and add extra chopped nuts if desired.

Cool completely at room temperature for about 4 hours or refrigerate until set.

Once set, lift toffee from the pan using parchment paper, slice into pieces, and enjoy!