Fill a medium-sized saucepan with butter, sugar, salt, and water. Stick a candy thermometer into it.
Cook on medium-low heat, stirring gently and frequently until the sugar completely dissolves and the mixture comes to a boil.
Continue cooking and stirring regularly until the candy thermometer reads 290 F. The toffee should be a nice golden color.
Remove from the heat immediately and stir in the vanilla extract.
Pour into an 8" square baking dish prepared with greased parchment paper.
Let the toffee sit for a couple of minutes and then top with chocolate chips.
Cover with foil and let sit for five minutes for the chips to melt.
Spread the chocolate chips evenly over the top of the toffee and cover with chopped pecans.
Refrigerate for at least two hours.
Break into pieces by placing the toffee square in a Ziploc bag, turning it upside down, and hitting it with a hammer or a rolling pin. (Make sure you protect your countertop by putting the bag onto a cutting board or towel before hitting it.)
Notes
Store in an airtight container at room temperature for a couple of weeks. Or, freeze for several months.DO NOT step away from the pot or you risk burning the candy and having to start all over again.It may take a while to get to the correct temperature, but don't be tempted to raise the heat. Low and slow is the best way to go here. You are much more likely to burn the toffee on higher heat.