Spray bottom of a jellyroll pan with cooking spray.
Sprinkle pecan pieces evenly over the pan.
In a heavy-bottomed pot over medium heat, begin melting butter.
Once a film of butter coats the bottom of the pan, add brown sugar.
Stir constantly, allowing the mixture to boil.
When mixture pulls away from sides of the pan, insert candy thermometer and continue stirring.
When mixture thickens and approaches hard ball stage (about 260F), stir more quickly and vigorously.
As soon as it hits hard crack stage (about 300F) remove from heat.
Continue stirring and add vanilla.
Stir quickly and thoroughly to incorporate vanilla.
While mixture is still very hot, quickly pour over pecans in prepared pan.
Tilt pan to spread mixture if it is not evenly distributed.
Quickly unwrap Hershey bars and place on top of hot toffee.
Let chocolate bars sit for 5 minutes.
When soft enough to spread, use a knife to spread chocolate evenly over top.
Before chocolate cools, sprinkle evenly with optional ground pecans.
Let toffee sit overnight at room temperature.
Cut into squares or break into irregular pieces.
Makes about 3 dozen (2-inch) pieces of toffee.
Nutritional Information: per piece: 244 calories, 18g fat, 116mg sodium, 30mg cholesterol, 66% of calories from fat.
** Dallas Morning News -- Food section -- 22 Dec 96 ** Scanned and formatted for you by The WEE Scot -- paul macGregor