Dark Chocolate Fudge

2 Tbsp. butter or margarine
3 1/2 cups sugar
1/2 teaspoon salt
1 1/2 cups walnuts or pecans

4 ounces unsweetened chocolate


8 ounces bittersweet or semisweet chocolate
1 1/2 cups half and half
1/4 cup light corn syrup

2 tsp. Vanilla

Smoothly line an 8 or 9 inch square pan with foil.  Lightly butter foil.  In a 3 to 4 qt pan, mix half and half, sugar, corn syrup and salt.  Stir occasionally over high heat until simmering,     about 3 minutes.  With a brush dipped in water, frequently wipe off beads of syrup that form on the sides of the pan.  Reduce heat to medium.  Add bittersweet and unsweetened  chocolate; gently stir until chocolate melts and mixture begins to simmer, 3 to 6 minutes.  Insert a candy thermometer into mixture.  Boil, occasionally stirring and washing sides of pan with  wet brush, until mixture reaches 235 degrees (or a drop of candy spooned into cold water forms a soft ball that flattens when removed from water), 30 to 40 minutes longer.  Immediately pour fudge mixture into a 10 by 15 inch rimmed pan. Dot with 2 tablespoons butter and vanilla.  Let stand undisturbed until a thermometer inserted in center of candy registers 115 degrees (pan is warm to touch), 20 to 30 minutes.  With a wide metal spatula, scrape mixture back and forth in pan until it becomes smooth and glossy and starts to thicken and mound but is still soft and malleable, 4 to 10 minutes.  Add nuts and mix just enough to distribute.  Scrape fudge into foil-lined pan.  Let stand until firm to touch, at least 2 hours.  Invert pan to release candy.  Peel off foil.  With a sharp knife, cut fudge into 1 inch squares and serve.  Or wrap the uncut fudge airtight and store at room temperature up to 1 week.