Line a 9x9x2-inch baking pan with foil, extending foil over edges of pan. Butter foil; line with chocolate bars. Set pan aside.

In a heavy 2-quart saucepan combine sugar, corn syrup, and water. Cook over medium-high heat to boiling, stirring constantly with a wooden spoon to dissolve sugar. This should take 5 to 7 minutes. Avoid splashing mixture on sides of pan. Carefully clip candy thermometer to pan. Cook over medium heat, without stirring, to 260 degree F, hard-ball stage. Mixture should boil at moderate, steady rate over entire surface. Reaching hard-ball stage should take about 15 minutes.

Remove pan from heat; remove thermometer. In a large mixer bowl, immediately beat egg whites with a sturdy, freestanding electric mixer until stiff peaks form (tips stand straight).

Gradually pour hot mixture in a thin stream (slightly less than 1/8inch diameter) over egg whites, beating on high speed and scraping bowl occasionally. This should take about 3 minutes. (Add mixture slowly to ensure proper blending.) Add unsweetened chocolate and peppermint extract. Continue beating on high speed, scraping bowl occasionally, just until candy starts to lose its gloss. When beaters are lifted, mixture should fall in a ribbon, but mound on itself and not disappear into remaining mixture. Final beating should take 5 to 6 minutes.

Immediately spread over chocolate bars in prepared pan. Sprinkle with crushed candies. When firm, lift out of pan; cut into 1-inch squares. Store tightly covered. Makes 81 pieces.

Up to 3 days ahead prepare divinity. Store at room temperature in a tightly covered container.