Directions

1. Make the cake: Preheat oven to 300 degrees, with rack in center. Butter two 6-inch heart-shape cake pans. Line bottoms with parchment paper; butter parchment. Dust with cocoa powder, and tap out excess; set aside. Melt chocolate in a heatproof bowl set over a pan of simmering water, stirring often; set aside.
2. Put butter and 1/3 cup sugar into the bowl of an electric mixer fitted with the paddle attachment. Mix on medium speed until pale and fluffy, about 2 minutes. Mix in yolks, then vanilla and melted chocolate. Reduce speed to low. Mix in flour. Transfer batter to a large bowl.
3. Put egg whites and salt into the clean bowl of an electric mixer fitted with the whisk attachment. Beat on low speed until foamy. Raise speed to medium-high; gradually beat in remaining 2 tablespoons sugar. Raise speed to high, and beat just until stiff peaks form. Stir half the egg whites into the chocolate mixture. Using a rubber spatula, gently fold in remaining egg whites.
4. Divide batter between prepared pans. Tap firmly on counter to remove any air bubbles. Bake until centers are just set, 16 to 17 minutes. Let cool completely in pans on a wire rack. Turn out cakes; remove parchment. Reinvert onto rack.
5. Trim cakes flat. Warm jam in a small saucepan over medium-low heat, stirring occasionally, until slightly runny. Stir in liqueur, if desired. Spread warm jam over 1 cake layer. Top with remaining layer.
6. Make the ganache: Put chocolate into a large heatproof bowl. Bring cream just to a boil over medium-high heat; pour over chocolate. Let stand 10 minutes. Stir until smooth. Refrigerate, stirring every 10 minutes, until cooled and the consistency of corn syrup, about 30 minutes.
7. Slowly pour ganache over top and down sides of cake (use an offset spatula to spread evenly, if needed). Let stand 30 minutes. Arrange truffles over top of cake. Serve. Cake can be refrigerated in an airtight container up to 2 days.