Line a 10×15-inch jelly roll pan with aluminum foil.  Generously butter the foil.  Set aside.

Clip a candy thermometer to the side of a large, heavy-bottom skillet.  Do not allow the tip to touch the bottom of the pan. Place the pan over medium heat.

Add and melt the butter.  Stir in the sugar, corn syrup, and heavy cream.  Bring to a full rolling boil, stirring constantly.

Cook, continuing to stir until the sugar is turning a golden color. Continue to cook, stirring constantly, until the toffee reaches 295-305 degrees on the candy thermometer.  This is a hard crack stage – about 10-15 minutes.

Remove the pan from the heat and whisk in the salt and vanilla.

Carefully pour the mixture onto the prepared pan.  Use an offset spatula to spread it out evenly.

Immediately sprinkle the top of the toffee with the milk chocolate chips.

Allow the chips to melt for at least 2-3 minutes.

Spread evenly over the toffee.  Sprinkle the top of the chocolate with the toasted, chopped pecans.

Allow the toffee to cool completely.  Break into serving-size pieces.

Store in an airtight container in the refrigerator for up to three months.