This is a super rich bittersweet chocolate cake with just enough flour to hold it all together. If you don't have a heart-shaped pan, you can make the cake in a round pan and cut it into a heart afterwards. Or not!
To Make the Cake
Grease the pan and line the bottom with parchment paper.
Preheat the oven to 300 degrees F.
Melt the chocolate with the butter, in a bowl over simmering water. Stir occasionally until melted. Remove from the heat to cool slightly.
Whip the egg yolks, brandy and sugar in an electric mixer until thickened and creamy. Fold in the cooled chocolate mixture. Whisk the flour and baking soda together and sift it over the egg yolk mixture.
Fold just until all the flour is blended into the batter.
In a clean dry bowl with a clean beater, whisk the egg whites and salt until they form soft peaks. Fold one quarter of the egg whites into the chocolate mixture to lighten it. Fold in the remaining egg whites just until blended.
Pour the mixture into the prepared pan and bake for 50 to 60 minutes, or until the cake is just firm to the touch. Cool the cake in the pan on a rack.
To Make the Glaze
Melt the chocolate with the heavy cream in the top of a double boiler over simmering water. Stir until smooth and melted. Let the glaze cool at room temperature until it has a soft, spreadable consistency.
Turn the cake out of the pan. Cut the round cake into a heart if desired. Lightly spread the glaze over the cake. Store and serve at room temperature.