Preheat your oven to 350°F (175°C). Line a 9x13-inch baking dish with parchment paper, allowing some overhang for easy removal later.
Spread the coarsely chopped pecans evenly on a baking sheet. Toast them in the preheated oven for about 8-10 minutes, or until they are fragrant and golden. Set aside to cool slightly.
In a medium saucepan over medium heat, melt the unsalted butter. Once melted, add the granulated sugar and kosher salt. Stir continuously until the mixture comes to a boil, then reduce the heat to medium-low.
Continue to stir the mixture for about 5-7 minutes, until it turns a deep golden brown color. Be careful not to burn the mixture, as it can go from perfect to burnt very quickly.
Remove the saucepan from the heat and stir in the vanilla extract. Then, fold in the toasted pecans until they are well coated with the toffee mixture.
Quickly pour the toffee mixture into the prepared baking dish, spreading it evenly with a rubber spatula. Allow it to cool for about 5 minutes.
Sprinkle the milk chocolate chips evenly over the warm toffee. Let them sit for a couple of minutes to soften, then use the spatula to spread the melted chocolate evenly across the surface.
Allow the toffee to cool completely at room temperature. Once it has set, use the parchment paper to lift it out of the baking dish and cut it into pieces.