Cut chocolate fine; melt in double boiler over lukewarm water (115 degrees F).
Slice 1 cup of the almonds in halves lengthwise; coarsely chop
remainder of nuts.
Melt butter or margarine in heavy frying pan; add sugar, the almond halves, corn
syrup and water; stir until sugar is blended and no undissolved sugar adheres to
sides of pan. Cook very slowly until small amount in cold water separates into hard
but not brittle threads (290 degrees F). Stir occasionally to prevent burning.
Add vanilla extract.
Pour to 1/4-inch thickness into a 10 x 15-inch buttered
pan or individual molds.
When cool, spread melted chocolate evenly over the top.
Sprinkle with remaining chopped almonds.
When hard, break into pieces; store in a tightly covered container
between wax paper layers.