Grind the almonds finely in a rotary hand grater.
Put the grated almonds in a larger bowl and add the egg white and sugar. First with a fork, then by hand, work into a soft and slightly sticky cookie dough.
Divide the ball of dough into two halves. Work the cocoa powder into one half. Be patient, this step requires a little patience. Expect your hands to be caked with cocoa powder, but don't worry, you can simply wash them under warm water afterwards.
Roll both doughs into long and equally thick cylinders. Place them side by side, leaving about 1 inch (2.5 cm) of space between them.
Using a dough scraper or a knife, cut the cylinders into equal-sized pieces. Slice both halves of the dough in one go, this will give you the same number of white and cocoa bits.
Mushroom caps: Roll the cocoa piece into a ball. Take a wooden spoon with a smaller handle diameter. Carefully make an indent in the ball with the end of a round wooden spoon handle.
Mushroom stems: Also, roll the white piece into a ball and form it gently into a cylindrical shape. Pull the top part into a point. Slightly flatten the bottom to make the mushroom stand up.
Lastly, put the stem, pointy side up, into the hole in the mushroom cap and press slightly.