ready in 4 h. 55 min.
Combine half the flour with the yeast and about 175ml of the water in a large mixing bowl.
Mix well to form a very thick batter, then allow it to rest for roughly 2 hours until it has risen and then deflated.
Add the remaining flour, water, the salt, treacle, butter and caraway seeds, mixing until you have a dough.
Shape into a rectangle, then dust the inside of a 900 g | 2lb loaf tin with a little extra rye flour and fit the dough inside. Allow it to rise for 2 hours.
Line a baking tray with parchment, then turn the risen dough carefully on it. Bake for 30 minutes until risen. Remove and allow to cool completely on a wire rack.
When ready to serve, slice thinly into rectangular slices, removing any uneven crusts and arrange stacked on a plate lined with a napkin.
Garnish with the parsley and red onion slices.