Line an 8 inch square pan with buttered parchment paper.

In a medium heavy saucepan stir together sugar, cocoa and salt, then add the milk and stir with a wooden spoon.

Cook over medium heat stirring continuously until mixture starts to boil, approximately 15 minutes.

Turn heat to low medium and continue to cook without stirring until temperature reaches 234 ?F (112 ?C), approximately 30 minutes.

Remove pot from heat, add the butter and vanilla. Do not stir. Cool to room temperature (110?F/43?C), approximately 30 minutes.

Beat with a wooden spoon just until mixture begins to lose some of its gloss (approximately 6-8 minutes).

Spread quickly in prepared cake pan and let cool completely, even overnight.

Cut into squares. Store in an airtight container at room temperature.