2 cups granulated sugar
1/2 cup evaporated whole milk, unsweetened
1 1/2 tablespoons lemon juice
1/4 teaspoon salt
1 (2-inch) piece lemon zest
4 tablespoons butter (not margarine)
1/2 to 1 teaspoon lemon extract (optional)
1/2 cup chopped nuts (optional)
4 drops yellow food coloring (optional)

Butter the upper sides of a 2-quart saucepan. Put all ingredients except butter and the optional ingredients into the saucepan. Grease and line a 10 x 5-inch pan. Freeze all the butter. Fill the kitchen sink with 1/2 inch of water.

Dissolve the sugar. The mixture may look curdled, but it will turn out fine. Stir constantly with a wooden spoon over low heat until the spoon glides smoothly over the bottom of the an. 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 it, and it should be slightly chewy. The temperature will be approximately 236 degrees F to 244 degrees F.

Remove saucepan from heat and place it in the sink. Add frozen butter without stirring, then allow the fudge to cool.

Stir when lukewarm and skin forms on top (110 degrees F). Add food coloring and check flavoring. Add optional lemon extract if desired. Remove zest, then agitate in a food processor or with an electric mixer and not by hand. Pause frequently to allow fudge to react. Watch for fudge to thicken, lose its sheen, become light in color or streaked with lighter shades, 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 when processor is stopped. 

Add optional chopped nuts just before you pour. Pour, score and store when cool in airtight container in refrigerator or at room temperature. Yields 1 pound. This recipe is not easily doubled, but it can be frozen.