Start by gathering all your ingredients: chopped nuts, granulated sugar, vanilla extract, butter, salt, water, chocolate chips, and optional flaked sea salt. Line a 9x9 inch baking dish with parchment paper to prevent sticking.

Spread 1 cup of your chosen chopped nuts evenly across the bottom of the dish.

In a medium saucepan, combine butter, granulated sugar, water, and salt over medium heat. Stir frequently until the butter melts and sugar dissolves, about 5 to 7 minutes.

Attach a candy thermometer to the saucepan and cook until it reaches 300°F, around 10 to 15 minutes.

Once the toffee reaches 300°F, remove from heat and stir in the vanilla extract.

Pour the hot caramel mixture over the chopped nuts evenly. Cool for about 2 minutes.

Sprinkle chocolate chips over the warm caramel layer, cover with foil, and let sit for about 4 minutes.

Swirl the melted chocolate gently with a spatula and sprinkle additional chopped nuts and flaked sea salt on top.

Allow the toffee to cool at room temperature for about 4 hours until set.

Carefully lift the toffee out of the dish using the parchment paper overhang and cut into squares or break into pieces.