Cut the soft butter into cubes and stir in a bowl until the butter gets creamy. While mixing add the sugar and vanilla extract as well as the eggs one by one. Now, fold in the salt and lemon juice and stir. Flour and baking powder you add at the end. The dough should be very heavy and a bit sticky. If this is not the case add flour in tablespoons.
Put large portions of dough in the palm of your hand, roll it into a ball and put it then on the baking tray and flatten gently by pressing on top. The cookies should be approximately 5 cm in diameter. Leave space between the cookies as the dough expands while baking. Bake the cookies at 180 °C circulating heat for around 12 minutes until they are golden brown on the sides and still light in the middle.
Decoration: To prepare the frosting put the powdered sugar in a small bowl or cup and add the hot water bit by bit while stirring the mass with a spoon until it becomes smooth (not liquid). After the cookies cooled off spread 1 tsp of frosting on each cookie. Spread it even with a butter knife. Melt the chocolate coating over a warm water bath now. Once it is liquid draw lines across the cookies by putting a bit chocolate on a spoon and swing it back and forth over the cookies to create the chocolate pattern. Let the chocolate cool off and enjoy your cookies...
Change the decoration as you like. For example you could coat the cookies half with chocolate and half with frosting to get a half and half cookie. Please note if you do this decoration variation you need less frosting and more chocolate coating than the recipe says. Of course you can also enjoy the cookies without decoration.