Butter a large baking sheet and a metal spatula. In a heavy 5-6 quart saucepan combine water, sugar, and corn syrup and bring to a boil over moderately high heat, stirring until sugar is dissolved. Boil syrup, without stirring, until it registers 310F. on a candy thermometer. Remove pan from heat (syrup will be very hot). Carefully add baking soda and salt and, working quickly, stir until syrup foams and thickens. Stir in almonds and pour mixture onto prepare baking sheet, spreading with prepared spatula. Cool brittle 5 minutes and sprinkle chocolate evenly over it. Let chocolate melt, about 5 minutes, and spread it with a clean spatula. Chill brittle on baking sheet until chocolate hardens. Loosen brittle with a clean spatula from baking sheet and, holding brittle underneath with palms of hands to avoid smearing chocolate, drop from height of a few inches onto work surface to break into pieces. Transfer brittle, separating it with layers of wax paper, to airtight container. Brittle keeps, covered and chilled, 2 weeks. Makes about 1 1/2 pounds. Gourmet December 1994