Crumble the cold butter into the flour, powdered sugar, vanilla, and salt until you get a sawdust-like consistency.
Add egg and water and quickly knead the dough together until combined.
Do not over-knead the dough!
Divide the dough into 3 equal parts, then combine two of the parts again, so you now have a small portion (1/3 of the dough) and a large portion (2/3 of the dough).
Add 1 tbsp of wheat flour to the small portion and quickly knead it together.
Add 2 tbsp of cocoa to the large portion and quickly knead it together.
Chill the dough for about 30 minutes to make it firmer and easier to work with.
Divide the light dough into 14-16 balls (approx. 15-16 grams) and roll 5 smaller balls from each light dough ball. These will be used as paws and head.
Divide the dark dough into 14-16 balls (approx. 30-32 grams) and roll them round. Flatten them slightly and use a wire rack or the back of a knife to create a turtle shell pattern, then place a shell on top of the paws and head.
Bake the turtles in the oven at 180 degrees Celsius (356 degrees Fahrenheit) conventional oven for about 15-17 minutes.
Remove the cookies and let them cool completely.