Line the inside of a 9x5 inch loaf pan with nonstick foil.

Place unsweetened chocolate, milk chocolate and vanilla in a metal bowl; set aside.

Combine sugar, condensed milk, water, cream, salt (if using) and butter in heavy 3 to 3 ½ quart saucepan. I like to grease the sides of the saucepan to help prevent sugar crystals from forming.

Stir over medium-low heat (without scraping sides) until butter is melted and sugar dissolves. Brush down the sides of the pan with a damp pastry brush to keep sugar crystals from forming.

Increase heat to high and bring mixture to rolling boil. Don't let it boil over! It will foam and rise quite a bit, so lift it from the heat if this starts to happen.

Reduce heat to medium-high and cook, stirring slowly, until a candy thermometer registers 230F. Time will vary due to humidity levels, stoves, pots, etc., but keep the mixture at a steady boil and a slowly rising temp. It might hover around 220 for a while. When it hits 230 it should be fragrant and just slightly off white.

Without scraping the brown residue that forms on the bottom of the saucepan, pour boiling mixture over the chocolate and stir stir until chocolate melts. Mix in the almonds and transfer to the loaf pan, smoothing the top.

Transfer fudge to prepared pan and smooth top. Sprinkle with reserved nuts. Refrigerate uncovered until firm enough to cut, about 2 hours.

Lift fudge from pan and cut into pieces