Make sure the butter is at room temperature. Put the ground almonds in a bowl with the powdered sugar and the butter. Knead well.
Now add the rose water. First take only 4 tablespoons and knead everything well. If the marzipan is too firm, add more rose water until it has the firmness you want.
When your marzipan is ready, roll small balls and roll them in cocoa. The potatoes look even more beautiful if you cut them into a triangle at one point.