Beat the egg whites and salt with the whisks of the hand mixer until stiff. Let the sugar trickle in. Continue beating until the sugar has dissolved and a shiny mass has formed. Pour the beaten egg whites into a piping bag with a perforated spout. Line a baking tray (32 x 39 cm) with baking paper.
Spray half of the beaten egg whites onto the baking tray in approx. 20 flat tuffs as a mushroom hat. Spray the rest of the beaten egg whites as stems in small, high tuffs onto the baking tray, while lifting the piping bag. Press the resulting tip slightly flat again. Bake in a preheated oven (electric cooker: 125 °C/ convection oven: 100 °C/ gas: not suitable) for approx. 45 minutes. Turn off the oven and let the tuffs cool down overnight. Chop the chocolate and melt over a warm water bath. Sprinkle a large plate with plenty of sugar. Remove the tuffs from the baking paper. Spread large, flat tuffs with chocolate on the underside. Press a small tuff into each tuff as a stem.
Chop the chocolate and melt over a warm water bath. Sprinkle a large plate with plenty of sugar. Remove the tuffs from the baking paper. Spread large, flat tuffs with chocolate on the underside. Press a small tuff into each tuff as a stem. Leave to dry upside down on the plate sprinkled with sugar. Dust meringue mushrooms with cocoa powder for serving
Waiting time approx. 12 hours