Start by gathering all your ingredients: chopped pecans or almonds, sugar, vanilla, butter, salt, chocolate chips, and water. Line a 9×9 inch baking dish with parchment paper. Spread 1 cup of chopped pecans evenly on the bottom of the prepared baking dish to form a base for the toffee.

In a pot, combine 1 cup (226 grams) of butter (cut into pieces), 1 cup (200 grams) of granulated sugar, 1/4 cup (60 ml) of water, and 1/2 teaspoon of salt. Set the pot over medium heat and stir frequently until the mixture melts and begins to bubble. Attach a candy thermometer to the pot to monitor the temperature of the mixture, aiming for the hard crack stage at 300°F.

Continue stirring the mixture occasionally as it heats up, watching the thermometer closely. Once the mixture reaches the desired temperature of 300°F, promptly remove it from the heat. Carefully stir in 1 teaspoon of vanilla, ensuring it is thoroughly mixed into the caramel.

Pour the hot caramel mixture over the pecans in the prepared baking dish, spreading it out evenly with a spatula. Allow the caramel to cool for about 2 minutes, then generously sprinkle chocolate chips evenly over the warm caramel. Cover the dish with foil or a baking sheet to trap heat and allow the chocolate to melt.

After about 4 minutes, uncover the dish and gently swirl the melted chocolate using a knife or spatula to create an attractive pattern. Finely chop a handful of pecans and sprinkle them on top of the melted chocolate. For additional flavor, you may optionally sprinkle a small amount of flaked sea salt on top. Allow the toffee to cool completely for about 4 hours, or place it in the fridge to speed up the process.

Once the toffee has set and is cool to the touch, remove it from the pan by lifting the parchment paper. Cut the toffee into pieces with a sharp knife or break it apart with your hands. Serve and enjoy your homemade toffee!