In a cup combine boiling water, black treacle or molasses, barley malt extract. Then in a mixing bowl mix both flours, yeast, salt, ground coriander and sunflower seeds or chopped walnuts. Create a well in the center and pour in the liquid mixture together with oil and ⅔ of the tepid water. Mix well adding more water if the mixture if too dry. (It will vary depending on the humidity in the house.)
Rest for 5 minutes, then knead for 1 minute. Take it out of the bowl and knead it for at least 5 minutes on a floured surface. Then cover with a cloth and let it rise for 1.5 hours in a warm place.
Shape the dough into a boule (ball) using a simple stretch and fold method. Lightly stretch each side of the dough and keep tucking them in until you've form a ball. Place it on a floured surface seams side down, sprinkle with more flour, cover it and let it rise for another hour.
Preheat the oven to its maximum temperature (260C/500F) with the Dutch oven in it.
Before placing the dough in the preheated Dutch oven slash a cross on top with a sharp knife. Carefully drop the dough in the Dutch oven, cover with a lid and baked covered for 20 minutes. Then take the lid off and bake for 15-20 minutes until dark and the top is crispy. Cool on a wire rack before slicing.