Butter a 12 by 18-inch baking pan. Cover 2 large cutting boards or cardboard pieces with parchment paper. Set aside.
In a medium saucepan, melt butter. Remove from heat and stir in sugar, corn syrup, and 3 tablespoons water. Cook, stirring occasionally, until the mixture reaches 300 degrees F on a candy thermometer. Remove from heat, stir in 1 cup almonds, and pour out into prepared pan, spreading the mixture with the back of a spoon to fill the pan.
Before the candy hardens, but when it is firm enough to handle, turn it out onto parchment-lined board. Allow to cool completely.
Wipe the surface of the candy with a damp paper towel to remove excess butter, and allow to dry.
Use a small offset spatula to spread half the chocolate quickly over candy. Scatter 1/2 cup of the remaining almonds over chocolate. Cover with parchment paper and place second cutting board on paper. Turn candy over onto second surface. Remove top board and paper, and quickly spread candy with remaining chocolate and scatter on remaining 1/2 cup almonds. Refrigerate for 20 minutes to set chocolate.
Break candy into 2-inch pieces. The candy may be stored in an airtight container; use parchment paper to separate layers. Candy will keep at cool room temperature for up to 1 week.
How to Temper Chocolate:
In a heatproof bowl or the top of a double boiler, melt coarsely chopped chocolate over a pot of simmering water. The chocolate should register 115 to 120 degrees F on an instant-read thermometer.
Remove bowl from simmering water. Let cool, stirring occasionally, until it reaches a temperature of about 82 degrees to 86 degrees (depending on the variety of chocolate you are using) on an instant-read thermometer. At this point, the chocolate will begin to set around the edges of the bowl.
Return the bowl to the pot of hot, but no longer, simmering water for a few seconds at a time until it reaches a temperature of 88 degrees to 91 degrees F. Be sure not to allow chocolate to become hotter than 91 degrees F as this will make it necessary to repeat the entire tempering process.
(c)2003 Martha Stewart Living Omnimedia, Inc. All Rights Reserved.