Prep pan: Line a 15x10x1-inch baking pan with foil, extending over edges.

Make toffee: In a 3-quart saucepan melt butter. Stir in sugar, corn syrup, and 1/3 cup water. Cook over medium-high heat to boiling, stirring until sugar is dissolved. Avoid splashing onto sides of pan. Clip candy thermometer to pan. Be sure the bulb is well-covered and not touching bottom of the pan.

Cook: Cook over medium heat, stirring frequently until thermometer registers 290 degrees (soft-crack stage), about 15 minutes. (It should boil at a moderate, steady rate over entire surface). The mixture will turn golden brown.

Coat: Remove thermometer and pour mixture into prepared baking sheet; spread evenly. Cool 5 minutes or until just set. Then, sprinkle chocolate atop and let stand for about two minutes. Spread chocolate onto toffee. If desired, top with nuts & press into chocolate.

Cool: Cool several hours or until set. If necessary, place in refrigerator.

Break: Holding foil, lift candy out of the pan. Break into pieces. To store, layer candy in an airtight container.