Knead 300 g flour, sugar, butter in pieces, egg and 1-2 tbsp. cold water first with the dough hooks of the mixer, then quickly with your hands to a smooth dough. Wrap in foil and refrigerate for about 1 hour.
Line two baking trays with baking paper. Roll out the dough on a floured work surface until it is about 3 mm thin. Cut out a total of 4 circles (approx. 22 cm Ø), knead the remaining dough in between and roll out again.
Cut each circle into 8 triangles.
Preheat oven (electric cooker: 200 °C/circulating air: 175 °C/gas: see manufacturer). Place 1 tsp. jam on the broad side of each of the resulting dough triangles and roll up towards the top. Place croissants on the baking trays.
Bake in a hot oven for about 12 minutes one after the other. Remove and let cool off. Stir icing sugar and lemon juice until smooth. Spread a thin layer on the croissants, roll them in coconut flakes and let them dry.