Prepare a 9x9 inch baking dish lined with parchment paper for easy removal.

Spread 1 cup of chopped pecans evenly on the bottom of the lined baking dish.

In a heavy-bottom saucepan, combine butter, granulated sugar, water, and a pinch of salt. Heat over medium heat, stirring until the mixture starts bubbling (about 5-7 minutes).

Attach a candy thermometer and heat until the mixture reaches 300°F (hard crack stage).

Remove from heat and stir in 1 teaspoon of vanilla extract.

Pour the mixture over the prepared pecans, spreading evenly.

Sprinkle chocolate chips over the hot toffee, cover with a towel, and allow chocolate to melt (about 4 minutes).

Gently swirl the melted chocolate into the toffee and sprinkle with additional chopped pecans.

Optionally sprinkle flaked sea salt over the top.

Allow the toffee to cool at room temperature for about 4 hours or refrigerate to speed up the process before cutting.