Without the marble slab and other goodies that fudge shops have that we don't, this recipes comes very close to slab fudge.

2 1/2 Pound Batch
4 cups superfine granulated sugar
1/2 cup less 2 tablespoons corn syrup
1/3 teaspoon salt
1 1/4 cups whipping cream 
1 1/2 teaspoons vanilla extract (optional)
1/3 cup cocoa (for chocolate fudge)
3/4 cup peanut butter (for peanut butter fudge)
1 cup chopped nuts (optional)

6 1/4 Pound Batch
10 cups superfine granulated sugar
1 cup plus 2 tablespoons light corn syrup
3/4 teaspoon salt
3 cups whipping cream
4 teaspoons vanilla extract (optional)
3/4 cup plus 2 tablespoons cocoa (for chocolate fudge)
2 cups peanut butter (for peanut butter fudge)
2 1/2 cups chopped nuts (optional)

Use a 3-quart saucepan for the small batch or an 8-quart stockpot for the large batch. Measure all ingredients including optional cocoa and/or peanut butter, but not the other flavorings or optional nuts. Put into the saucepan; butter upper sides of the saucepan. Grease an 8-inch square pan for the small batch or a jellyroll pan for the large batch. Fill the kitchen sink with 1/2 inch of water.

Dissolve sugar, stirring constantly with a wooden spoon over low heat until butter melts and the spoon glides smoothly over bottom of pan. Increase heat to medium and bring to a boil. Wash down any crystals that may have formed with a pastry brush dipped in hot water, using as little water as possible.

Clip a candy thermometer to the side of the saucepan. Reduce heat while retaining boil. Stir no more than necessary. Test in ice water when mixture thickens and bubbles become noisy. A ball, formed in ice water, should hold its shape until heat from your hand begins to flatten t and it should be slightly chewy, approximately 236 degrees F to 240 degrees F.

Remove saucepan from heat and place it in the sink. Add extract without stirring, then allow to cool. Stir when lukewarm and skin forms on top (110 degrees F).

Stir fudge thoroughly but not vigorously by hand, with electric mixer, or with food processor. Pause frequently to allow fudge to react. Watch for fudge to chicken, lose its sheen, become lighter in color or streaked with lighter shade, give off some heat, and suddenly stiffen. If mixing by hand, fudge will "snap" with each stroke; by mixer, mixer waves will become very distinct; by food processor, fudge will flow sluggishly back to center with processor stopped. Add any optional nuts before fudge totally candies. Pour, score, and store when cool in airtight container in the refrigerator or at room temperature. The recipe can be frozen.

NOTE: To make different flavors, use concentrated pure extracts. Use 1 (.125 fluid ounce) bottle for the small batch and 2 1/2 to 3 (.125 fluid ounce) bottle for the large batch.