Half rye, half strong white, a spoonful of caraway crushed in the mortar and a long cold ferment in the fridge. It goes into a tin because rye will not hold a shape by itself.
Wrap it in a cloth when it comes out and do not cut it for a day. I know. Do not cut it for a day.
What goes wrong
All rye. It works, but you get a brick, and I have made enough bricks for both of us.