In a medium, double boiler, add water to bottom pot and combine chocolate and butter in top pot or metal bowl that sits comfortably over pot. Bring water to a boil and lower heat.
Stir chocolate mixture over gently boiling water until melted and combined. Remove top pot/bowl from heat and let cool slightly. Beat in sugar, mixture will be coarse.
Add eggs, one at a time, beating thoroughly after each addition. Stir in vanilla. In a large bowl, combine flour, baking powder and salt.
Stir into chocolate mixture. Blend to make a smooth, yet stiff batter. Gently fold in nuts. Roll dough into an even ball, cut in half.
Roll each half into a 2-inch log; wrap in wax paper or plastic wrap. Chill dough for 30 minutes. Preheat oven to 300°F. Unwrap logs and slice into 1/2-inch circles. Using hands, shape chilled dough into 1 1/2-Inch balls.
Arrange on ungreased baking sheets. Bake for 15 - 18 minutes, or until firm.
Transfer sheets to a wire rack and let cookies cool on sheets.
Unsweetened chocolate, also known as bitter or baker's chocolate should be used in this recipe. Always use the type of chocolate specified in a recipe. Most types of chocolate are not interchangeable.
Try substituting raspberry, orange, almond or any flavored extract that compliments chocolate in place of vanilla.