Lightly coat a 9-inch square baking pan with cooking spray, then line it with parchment paper.

Scatter the chopped pecans evenly across the lined pan.

In a sturdy 3-quart saucepan, melt the butter with the sugar and salt over medium-low heat. Stir regularly until the sugar dissolves and the mixture begins bubbling.

Allow the mixture to boil, stirring occasionally, until it reaches the hard-crack stage—about 290–300°F.

Remove from the heat and stir in the vanilla.

Carefully pour the hot toffee mixture over the pecans in the baking pan.

Let it rest a few minutes, then sprinkle the chocolate chips over the top. Cover with foil and let the heat soften the chocolate for about 5 minutes.

Lift off the foil and spread the melted chocolate smoothly with an offset spatula.

Chill the toffee in the refrigerator for about 2 hours, or until completely firm.

Once set, lift the parchment from the pan and transfer the slab to a cutting board. Break it into bite-sized shards.

Store the toffee in an airtight container somewhere cool to maintain its crunch.