Begin by lining a 9x9 inch baking dish with parchment paper.

Spread 1 cup of chopped pecans evenly across the bottom of the prepared dish.

In a medium saucepan, combine 1 cup of butter, 1 cup of granulated sugar, 2 tablespoons of water, and a pinch of salt over medium heat.

Continue cooking until the mixture reaches 300°F (hard crack stage) and turns a golden amber color.

Stir in 1 teaspoon of vanilla extract cautiously as it may bubble.

Pour the hot toffee mixture over the prepared layer of pecans.

Allow the toffee to cool for about 2 minutes, then sprinkle 1 cup of chocolate chips on top.

Cover the toffee gently to let the chocolate chips melt for about 4 minutes.

Using a spatula, swirl the melted chocolate to create a marbled effect.

Let the toffee sit at room temperature for about 4 hours until fully cooled and set.