Preheat the oven to 356°F (180 °C). Grease and lightly flour a baking form in the shape of a heart. If you do not have one, you can use a regular tray and then carefully cut the cake in the shape of a heart.
Mix together the butter, powdered sugar, salt and add the yolks to the mixture all at once. Mix everything well and add the pre-melted in a water bath and cooled dark chocolate. Separately, beat the egg whites with a pinch of salt into powdered snow, gradually adding the sugar.
Mix 1/3 of the egg whites into the chocolate mixture. To the remaining whites, add the flour and mixture and gently homogenize everything. Pour the mixture in the form and put it to bake for about 40 minutes. Check for readiness with a stick. Cool the finished cake and remove from the form onto a grill.
Melt the couverture chocolate and mix with the rum flavoring. Pour it over the heart cake. Make a decoration of grated chocolate along the base of the cake, carefully sticking the chips to the cake.