Chop up squares of chocolate and put in heavy saucepan with sugar, salt, milk, and syrup.

Place over low heat and stir until mixture boils. This takes a while, about 20 minutes, so have a book to read while stirring.

Then cook to the stage where it will form a soft ball in water (234 degrees on a candy thermometer).

Remove from heat; stir in butter, and cool down to lukewarm.

Add vanilla and stir vigorously for about 5 minutes; turn into a large bread tin, buttered (a 9" x 9" pan works too).