Prepare a 9-inch square baking dish by spraying it with cooking spray and lining it with parchment paper.
Evenly spread the chopped pecans in a single layer on top of the parchment.
In a heavy-bottomed 3-quart pot, combine the butter, sugar, and salt.
Over medium-low heat, bring the mixture to a boil, stirring frequently to ensure the sugar dissolves.
Once the candy is boiling, stir occasionally until it reaches a temperature of 290°F to 300°F (143°C to 149°C) or reaches the "hard crack" stage on a candy thermometer.
Remove the pot from heat and gently stir in the vanilla extract.
Carefully pour the hot mixture over the chopped pecans in the baking dish.
Allow the candy to sit undisturbed for a few minutes, then sprinkle the chocolate chips evenly over the top.
Cover the baking dish with foil and let it sit for 5 minutes or until the chocolate chips have softened.
Remove the foil and use an offset spatula to gently spread the softened chocolate into an even layer.
Place the dish in the refrigerator and let the toffee cool completely, which typically takes at least 2 hours.
Lift the parchment paper out of the baking dish and transfer the toffee to a cutting board or solid surface.
Use a knife to break the toffee into smaller, bite-sized pieces.
Store the toffee in an airtight container in a cool place, and enjoy at your leisure.