Start by lining a baking sheet with parchment paper. This will help prevent the toffee from sticking once it’s cooled and make it easier to cut into pieces.
In a heavy bottom saucepan, combine the coarsely chopped pecans and the unsalted butter. Heat over medium heat, stirring occasionally, until the butter is completely melted.
Once the butter has melted, add the packed brown sugar. Stir continuously until the mixture begins to boil. Make sure to keep stirring to prevent the sugar from burning.
Using a candy thermometer, monitor the temperature of the mixture. You want it to reach 300°F (hard crack stage). This step is crucial for achieving that perfect crunchy texture.
Once the mixture reaches the desired temperature, remove it from heat and quickly stir in the vanilla extract. Be cautious, as the mixture will bubble up when you add the vanilla.
Carefully pour the toffee mixture onto the prepared baking sheet. Use a spatula to spread it evenly if needed. Let it sit for a few minutes until it starts to harden slightly.
While the toffee is still warm, sprinkle the milk chocolate chips over the top. Allow them to sit for a minute or two to soften, then use a spatula to spread the melted chocolate evenly over the toffee.
Allow the toffee to cool completely at room temperature. Once set, break it into pieces and enjoy!
