Grease jelly roll pan or half sheet pan then spread walnuts all over the pan. Set aside.
In a large 6-quart pot over medium-high heat, combine butter, sugar, water, and corn syrup. Bring mixture to a boil, stirring often.
Continue boiling and stirring until the candy mixture reaches 305 degrees F on a candy thermometer.
Immediately pour candy mixture over nuts in the greased pan.
Wait 2-3 minutes for the candy to set then sprinkle chocolate chips all over the top.
Allow the chocolate chips to sit for at least 5 minutes until the chocolate starts to melt then swirl the chocolate with the back of a spoon until it completely covers the toffee.
Allow the toffee to rest at room temperature for at least an hour until toffee is cooled and firm.