In 5-quart glass or ceramic microwave-safe bowl, combine sugar, half-and-half, syrup and salt. Cook on HIGH for 5 to 7 minutes until mixture comes to a full boil, stirring occasionally.
Set microwave-safe candy thermometer in place. Continue to cook on HIGH for 7 to 10 minutes or until temperature reaches 240 degrees F or soft ball stage (when a small amount of mixture dropped into a bowl of cold water forms a soft ball that flattens on removal from water).
Dissolve coffee in hot water; add coffee mixture, butter and vanilla extract to hot candy mixture, but do not stir. Cool without stirring to 110 degrees F or until outside of bowl feels lukewarm.
Meanwhile, lightly butter an 8-inch square baking pan. When mixture is cool, beat with a wooden spoon until fudge becomes thick and begins to lose its gloss. Stir in nuts. Pour fudge into prepared pan (do not scrape bowl as the mixture on the side may be sugary). Chill.
When firm, cut into squares.
Makes about 2 pounds.