Beat egg whites, lemon juice and salt until stiff. Add sugar, except 2 tablespoons, while stirring. Continue beating until the sugar has dissolved and the mixture is firm to cut. Carefully fold the grated coconut and remaining sugar into the egg white mixture with a dough scraper.
Pour into a piping bag without spout attachment. Line a baking tray with baking paper. Spray approx. 10 heaps of the coconut mixture on top. Leave a distance of 3 cm between each heap. Whisk the egg yolk and milk and brush the coconut heaps with it.
Bake in the preheated oven (electric oven: 200 °C/ gas: level 3) for about 10 minutes. Then lower the temperature to 175 ° C (gas: level 2) and bake for another 10 minutes. Remove the coconut macaroons and let them cool completely on a cake rack.
Coarsely chop the couverture with a knife. Melt in a hot water bath while stirring. Dip the cosmic macaroons with the bottom about 1/2 cm deep. Let dry on a cake rack.