Start by lining a 9×13-inch baking dish with parchment paper or a silicone mat to prevent sticking.

In a heavy-bottomed saucepan, combine the unsalted butter, granulated sugar, salt, and water. Cook over medium heat while stirring continuously until it reaches a deep golden brown color (300°F on a candy thermometer).

Once the toffee mixture has reached the desired temperature, immediately pour it onto the prepared baking dish and spread it evenly.

Allow the toffee to sit for approximately 2 minutes to slightly cool, then sprinkle the chocolate chips evenly over the top.

While the chocolate is still soft, sprinkle your choice of chopped nuts over the melted chocolate layer and press gently.

Let the toffee cool at room temperature for about 2 hours, or refrigerate for 30 minutes, then break into pieces.