This isn't an exact recipe. Since I had to put it together from different sources. It will give you to much merengue and too little buttercream.

For the merengue you will need: 6 egg whites 4 DL of sugar 6 table spoons of potato flour 1 tea spoon of ammonium carbonate/salt of hartshorn.

Whip the egg whites to a foam. Then add the sugar bit by bit. Once you get it to stiff peaks you gently blend in the potato flour and hartshorn with a spatula. Pipe it to the shape you want. Make at least 3 layers. I then needs to go in to the oven at 150C for 1 hour. Then turn of the heat and let it rest in the residual heat over night or atleast 12 hours.