Microwave 8 oz. chocolate in a glass bowl at HIGH 1 minute or until melted.
Combine sugar and water in a small heavy saucepan; cook over medium heat until sugar dissolves, stirring gently. Continue to simmer, without stirring, about 7 minutes or until syrup is golden, brushing down sides of pan with a pastry brush dipped in water; remove pan from heat. Carefully add cream (mixture will bubble). Return pan to low heat, and simmer, stirring until smooth. Stir in 1/4 tsp. fleur de sel. Remove from heat. Add cream mixture to melted chocolate; stir until smooth, and let cool. Cover and chill 3 hours or until firm.
Place cocoa in a bowl. Shape chocolate mixture into 1" balls (we used a 1" ice cream scoop); roll in cocoa. Place truffle balls on a baking sheet; chill until firm.
Place 12 oz. chocolate in top of a double boiler over simmering water until a thermometer inserted into chocolate registers 115°.* Remove top insert; working quickly, dip truffles in melted chocolate, coating completely. Lift out truffles with a small fork, letting excess chocolate drip off. Tilt double boiler insert, if needed, to make dipping and coating easier. Return top insert to heat every few minutes to keep chocolate at 115°. Transfer truffles to parchment paper. Sprinkle truffles lightly with additional fleur de sel. Let stand until chocolate coating is set.
*It's important to keep the saucepan of melted chocolate at 115° for coating the truffles. As your guide, use a candy or digital thermometer, easily found at your local cook store. Once this chocolate coating hardens on the candy, it will lend a nice crunch when you bite into it.