Sift the icing sugar. Beat the egg whites with the whisks of the hand mixer until stiff. Whip the icing sugar into the mixture by the spoonful. Take off 6 tablespoons (approx. 130 g) of egg white mass and mix with orange fruit.
Stir hazelnuts, vanillin sugar, cinnamon and rum into the remaining meringue. Sieve some icing sugar onto a work surface and roll out the hazelnut dough 1/2-1 cm thick. Cut out about 50 hearts and spread them on two baking trays lined with baking paper.
Knead the dough again and again and roll out again. Spread hearts with orange meringue. Bake in the preheated oven (electric: 150 °C/ gas: level 2) for 18-20 minutes. Let cool on a cake rack.
In the meantime cut out small hearts from the orange slices as desired. Warm the jam and pass it through a sieve. Spread orange hearts with jam and stick them on the cinnamon hearts. Leave to dry.
Store hearts cool and dry in tightly closed cans.