Beat the egg whites and lemon juice with the whisks of the hand mixer until stiff. Gradually add sugar and salt. Add the food colouring and fold in briefly to create a pink marbling. Pour the mixture into a piping bag with a large star-shaped spout. Line 2 baking trays with baking paper. Spray approx. 24 flat rosettes (3-4 cm Ø) on top
Allow both trays to dry together in the preheated oven (electric cooker: 100 °C/ circulating air: 75 °C/ gas: see manufacturer) for at least 3 hours. After half of this time, replace the upper tray in the lower rack and the lower one in the upper rack
Remove the sheets from the oven. Carefully melt the chocolate over a warm water bath, let it cool down. Whisk the butter with the whisk of the hand mixer until white-creamy. Stir in chocolate by the spoonful
Pour cream into a piping bag and squirt splotches onto the underside of half of the tuffs. Place the remaining tuffs on top and press down lightly. Shelf life maximum 1 week in a cool place, packed airtight. If unfilled, the tuffs will keep a few weeks longer.