Breaking up is easy to do, at least when it comes to delicious hard candy like this toffee.
To prepare pan: Spray 9-by-13-inch baking pan with vegetable spray, line with parchment, and spray again. (Use parchment overhang to remove cooledsheets; wrap in plastic, and store flat.)
Bring butter, sugar, water, and corn syrup to a boil over medium-high heat, stirring often, until dissolved. Cook, undisturbed, until it reaches 238 degrees on a candy thermometer. Add toasted pecan pieces; cook, stirring, until dark caramel, about 6 minutes more. Pour into pan, and let cool. Can be stored up to 1 week.