This is a slow cooker, but you don't have to stir in fact, you shouldn't while it's boiling. It balls at a fairly low temperature and smells heavenly while cooking. Use a 5-quart saucepan because, when it comes to a boil, it threatens to boil over. For a plain maple flavor eliminate vanilla.
1 cup heavy (whipping) cream
1 cup unsweetened evaporated milk
2-1/4 cups (1 pound) granulated white sugar
1 tablespoon plus 1/2 teaspoon light corn syrup
1 cup pure grade A Vermont maple syrup
1 cup walnuts or pecans or 1/2 cup of both
1 teaspoon baking soda
1 tablespoon butter, ice-cold
1-1/2 teaspoons vanilla extract (optional)
STEP 1: Prepare: Prewarm thermometer; use 5-quart saucepan; butter upper sides of saucepan; measure all ingredients but baking soda, and dump into saucepan. Measure out 1 teaspoon baking soda, but add only a pinch (1/8 teaspoon) to begin with. If maple syrup is not pure and mixture doesn't foam up high when it comes to a boil in step 3, add rest of teaspoonful. Grease and, if necessary, line a 8 X 8-inch pan. Fill glass with ice cubes and water and sink half-inch full of water.
STEP 2: Dissolve sugar, stirring constantly with wooden spoon over low heat until butter melts, gritty sounds cease, and spoon glides smoothly over bottom of pan. Increase heat to medium and bring to a boil.
STEP 3: Boil after washing down any crystals that may have formed with pastry brush dipped in hot water from thermometer bath, using as little water as possible. Introduce prewarmed thermometer. Reduce heat while retaining boil.
STEP 4: Test in ice-cold water when mixture thickens and bubbles become noisy. Ball, formed in ice water, should hold its shape until heat from your hand begins to flatten it and should be al dente slightly chewy. Approximately 236°F to 244°F (113.5°C to 118°C).
STEP 5: Shock by placing saucepan in sink.
STEP 6: Seed by adding, without stirring, 1 tablespoon ice-cold butter, and vanilla, if desired. Then allow to cool.
STEP 7: Stir when lukewarm and "skin" forms on top (110°F [43.5°C]). Return thermometer to its hot-water bath to soak clean. Stir fudge thoroughly but not vigorously by hand, with electric mixer, or with food processor. Pause frequently to allow fudge to react.
STEP 8: Watch for fudge to thicken, lose its sheen, become lighter in color or streaked with lighter shades, give off some heat, 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.
STEP 9: Add nuts.
STEP 10: Pour into an 8 x 8-inch pan. Score and store when cool in airtight container in refrigerator or at room temperature.
YIELD: 1 pound. Recipe is easily doubled and can be frozen.