HEAT OVEN TO 325 DEG F. CHOP UNSWEETENED CHOCOLATE. COMBINE 6 TBSP. BUTTER IN A SAUCE PAN WITH HALF THE CHOPPED CHOCOLATE. MELT AND STIR UNTIL SMOOTH. REMOVE FROM HEAT AND COOL COMPLETELY. BUTTER A 23 cm ROUND CAKE PAN. WITH AN ELECTRIC MIXER, SET AT MEDIUM SPEED, BEAT EGGS UNTIL FROTHY. STILL BEATING, ADD SUGAR. INCREASE SPEED TO HIGH AND BEAT UNTIL THICK AND PALE YELLOW. REDUCE MIXER SPEED TO LOW, AND BEAT IN 1.5 TSP. VANILLA AND SALT. BEAT IN WITH CHOCOLATE MIX. WITH A SPOON, MIX IN FLOUR. POUR INTO PREPARED PAN. BAKE UNTIL BROWNIE PULLS AWAY FROM EDGES OF PAN, ABOUT 35 TO 40 MINUTES, OR UNTIL A WOODEN PICK COMES OUT CLEAN. COOL IN PAN FOR 10 MINUTES, THEN TURN OUT ONTO WIRE RACK. COOL COMPLETELY. CHOP CANDY BAR. COMBINE REMAINING CHOCOLATE AND BUTTER IN A SAUCE PAN, OVER LOW HEAT. STIR UNTIL SMOOTH. REMOVE FROM HEAT. WITH ELECTRIC MIXER, SET ON LOW SPEED, GRADUALLY BEAT CONFECTIONERS SUGAR AND 0.75 TSP. VANILLA INTO MELTED CHOCOLATE MIX. SPREAD THIS FROSTING MIX OVER THE TOP OF THE BROWNIE. SPRINKLE WITH CANDY BAR PIECES. MELT WHITE CHOCOLATE OVER LOW HEAT. WITH THE TINES OF A FORK, DRIZZLE WHITE CHOCOLATE OVER THE BROWNIE, FIRST IN ONE DIRECTIONM THEN THE OTHER. MAKES 8 SERVINGS, EACH 560 CALORIES, 30 g FAT, 6 g PROTIEN, 114 mg SODIUM, 73 mg CARBS, 116 mg CHOL.