TO MAKE THE CAKE: melt the chocolate in a small saucepan over very low heat. Add 1/4 cup of sugar and the butter and stir until melted. Whisk in the egg yolks. Cook stirring constantly until mixture reaches 160~ on a candy thermometer. Set aside to cool. In a mixing bowl, beat the egg whites until stiff. Add the remaining sugar and beat until glossy. Whisk 1/3 of the egg whites into the chocolate mixture. Fold in the remaining whites. Rinse 4 4 oz. heart shaped molds or ramekins with water; DO NOT DRY. Divide the chocolate mixture among the molds. Refrigerate for 24 hours. TO MAKE THE SAUCE: Remove as much skin as possible from the pistachios. Rinse quickly with boiling water, drain and then remove as much of the remaining skin as possible. Place the nuts in a food processor and pulse until ground. Add 1/3 cup of sugar and the egg white and process until mixture forms a paste. Place 3 T of the pistachio paste in a medium sized saucepan (save the rest for another use). Add the milk and bring mixture to a boil over medium heat. Remove from the heat and let steep for 5 minutes. Strain through a fine mesh sieve into another medium size saucepan. Set aside. Whisk together the egg yolks and the remaining sugar until thick and light. Whisk in half the strained milk; then whisk the mixture back into the remaining milk. Cook the sauce over low heat, stirring constantly until thick enough to coat the back of a spoon; do not let the mixture come to a boil. Refrigerate for 24 hours. TO SERVE: Spoon a pool of the sauce onto the center of each of 4 plates. Run the tip of a small knife around the inside edge of the molds. Dip them briefly into hot water and invert them onto the plates. ----