Bring to a boil:

3 c. granulated sugar
1 1/2 c. milk
1/2 c. cocoa
Dash of salt

Bring all ingredients to a boil and stir constantly. Put on candy thermometer and let it come to boil again. Let boil until it reaches soft ball (240 degrees). Do not stir. When it comes to soft ball, remove from heat. Add:

1 tsp. vanilla
2 tbsp. butter

Do not stir. Let cool to 110 degrees (I usually only let it cool to 130 degrees). Stir until fudge loses its gloss (I don't stir quite that long, it might get too hard to pour). Then pour into buttered 9 x 9 inch square pan. Cool in refrigerator, cut into squares before it gets too hard, about 10 minutes later. Remove from pan after it is firm.