Prepare by lining a 9"x9" baking dish with parchment paper, spreading 1 cup of chopped pecans evenly on the bottom.

In a medium saucepan, combine butter, granulated sugar, water, and salt over medium heat, stirring continuously until melted and bubbling, about 5 minutes.

Insert a candy thermometer and cook until the mixture reaches 300°F, stirring occasionally, about 10-15 minutes.

Remove from heat and stir in vanilla extract; pour the caramel mixture over the prepared pecans.

Allow the caramel to cool for 5 minutes, then sprinkle chocolate chips on top and cover to let melt for 5-10 minutes.

Gently swirl melted chocolate over the caramel and sprinkle with chopped pecans and flaked sea salt if desired.

Let cool completely at room temperature for at least 4 hours, or refrigerate for 1-2 hours.

Lift the toffee out using the parchment paper and slice into pieces to serve.