- 10 ounces good-quality white chocolate (such as Lindt or Baker's), chopped
- 8 ounces semisweet chocolate, chopped
- 7 ounces semisweet chocolate, chopped
- 1 ounce unsweetened chocolate, chopped
- 3 tablespoons unsalted butter
- 1/3 cup sugar
- 2 tablespoons water
- 1 tablespoon light corn syrup
- 2 large egg whites
- 1/8 teaspoon cream of tartar
- 1/2 cup chilled whipping cream
- 1 teaspoon vanilla extract
- Turn two 15×10-inch baking sheets bottom side up. Dab butter on corners. Cover each pan bottom with parchment paper; press paper into butter to anchor.
- Stir white chocolate in top of double boiler over barely simmering water until melted. Spread white chocolate over 1 sheet of parchment. Stir semisweet chocolate in clean top of double boiler over simmering water until melted. Spread semisweet chocolate over second sheet of parchment. Chill both sheets until chocolates are dry but still slightly flexible when edge of parchment is lifted, about 3 minutes for dark chocolate and 5 minutes for white chocolate (do not let chocolate harden completely).
- Press heart-shaped cookie cutter about 3 inches long by 3 inches wide into chocolate, forming 12 hearts on each sheet (do not move or lifts hearts). Chill until firm, about 30 minutes.
- Combine both chocolates and butter in small saucepan. Stir over low heat until smooth. Cool slightly.
- Combine sugar, 2 tablespoons water and corn syrup in heavy small saucepan. Stir over low heat until sugar dissolves. Increase heat; boil until candy thermometer registers 238°F, tilting pan if necessary to submerge bulb of thermometer and brushing down sides of pan with wet pastry brush, about 4 minutes.
- Meanwhile, using electric mixer, beat egg whites and cream of tartar in large bowl until soft peaks form.
- Gradually add boiling syrup to whites, beating until firm peaks form and meringue is completely cool, about 5 minutes. Gradually fold lukewarm chocolate mixture into cooled meringue.
- Beat cream and vanilla in small bowl until firm peaks form. Fold into chocolate mixture. Chill until cold, about 1 hour. (Hearts and mousse can be made 1 day ahead. Cover separately; keep chilled.)
- Turn 1 sheet of hearts out onto work surface. Peel off parchment. Cut around hearts, if necessary, to free from sheet of chocolate. Place on baking sheet and chill; transfer trimmings to small saucepan and reserve. Repeat cutting out hearts from second sheet, reserving trimmings in another small saucepan.
- Arrange 12 hearts on baking sheet. Spread 1/4 cup of mousse over each, leaving 1/2-inch border. Top each with another chocolate heart. Refrigerate.
- Using fork, stir dark chocolate trimmings over very low heat just until melted. Using another fork, stir white chocolate trimmings over very low heat just until melted. Using another fork, stir white chocolate trimmings over very low heat just until melted. Dip tines of fork into dark chocolate; wave fork over hearts to form pattern. Repeat with white chocolate. Chill 1 hour to 8 hours. Serve cold.