Prep the pan: Line a large baking pan with parchment or foil and lightly spray with non-stick spray. Set aside.

Combine ingredients: In a large saucepan, combine water, corn syrup, salt, and sugar. Stir until the sugar is moistened. Wipe down stray sugar crystals from the side of the pan with a wet pastry brush if needed. Add the butter.

Cook the toffee: Heat over medium heat, stirring occasionally until it begins to boil. Once boiling, stop stirring. Attach a candy thermometer and cook until it reaches 290–300°F (hard crack stage).

Pour & cool: Carefully pour the mixture into the prepared pan. Let cool for 10 minutes, then blot excess butter from the surface with a paper towel to help the chocolate stick.

Add chocolate & nuts: Melt the dark chocolate and spread it evenly over the cooled toffee. Sprinkle chopped pecans on top. Allow to set completely.

Break & serve: Once set, break the toffee into pieces and enjoy!