Step 1

Line 8-or 9-inch square pan with foil, extending foil over edges of pan. Butter foil.

Step 2

Mix sugar, cocoa and salt in heavy 4-quart saucepan; stir in milk. Cook over medium heat, stirring constantly, until mixture comes to full rolling boil. Boil, without stirring, until mixture reaches 234°F on candy thermometer or until small amount of mixture dropped into very cold water, forms a soft ball which flattens when removed from water. (Bulb of candy thermometer should not rest on bottom of saucepan).

Step 3

Remove from heat. Add butter and vanilla. Do not stir. Cool at room temperature to 110°F (lukewarm). Beat with wooden spoon until fudge thickens and just begins to lose some of its gloss (about 7 minutes). Quickly spread in prepared pan; cool completely. Cut into squares. Store in tightly covered container at room temperature.