Spray a 9-inch square baking dish with cooking spray and line it with parchment paper.

Spread the chopped pecans evenly in a single layer on top of the parchment.

In a heavy-bottomed 3-quart pot, add the butter, granulated sugar, and kosher salt.

Place over medium-low heat and bring the mixture to a boil, stirring frequently to help dissolve the sugar.

Once boiling, reduce the stirring to occasional, slow, and even stirring.

Continue cooking until the mixture reaches 290°F to 300°F (hard crack stage).

Remove the pot from heat immediately after reaching the desired temperature and gently stir in the vanilla extract.

Carefully pour the hot toffee mixture over the spread pecans in the baking dish, ensuring an even layer.

Let the toffee sit undisturbed for a few minutes to slightly cool.

Sprinkle the milk chocolate chips evenly over the toffee surface and cover with foil for 5 minutes to soften the chips.

Remove the foil and gently spread the softened chocolate into an even layer.

Place the dish in the refrigerator to cool and harden for at least 2 hours.

Once hardened, lift the parchment paper containing the toffee out of the dish, transfer to a cutting board, and gently break into smaller pieces.