This bread is a lot like the bread my mother used to bake. She was a fantastic baker. Alas, I did not inherit the baking gene.
This is a Nigella Lawson recipe. I do not use the activated charcoal as I would not know where to even get it. See her note about this.
https://www.nigella.com/recipes/no-knead-black-bread
Reading the recipe, it doesn’t look like you need it. But you can apparently buy it at some spice and baking supply places.
https://spiceology.com/products/activated-charcoal/