LINE 8-inch-square baking pan with foil.
COMBINE sugar, evaporated milk, butter and salt in medium, heavy-duty saucepan. Bring to a full-rolling boil over medium heat, stirring constantly. Boil, stirring constantly, for 4 to 5 minutes. Remove from heat.
STIR in marshmallows, morsels, nuts and vanilla extract. Stir vigorously for 1 minute or until marshmallows are completely melted. Pour into prepared pan; refrigerate for 2 hours or until firm. Lift from pan; remove foil. Cut into 48 pieces.
HINT: For thicker fudge, use a 9 x 5-inch loaf pan; refrigerate for 3 hours.