This is based on a King Arthur Flour recipe.  The bread turned out well, but the top looked strange, as shown in the photo.  I made deep 2 x 2 cuts in a hashtag (#) pattern, and it made the top look very segmented.  The next time, I will make a simple cross-shaped cut.

This recipe uses a blend of barley, oats, rye, wheat, millet, and quinoa flakes sold by King Arthur Flour.

I used my own sourdough starter, which is 50/50 flour and water by weight.  I also used a baking steel and poured a cup of boiling water into a heated cast iron frying pan in the bottom of the oven to make steam to improve the rise and the crust.  I found the dough rose fairly slowly, perhaps due to a relatively cool winter kitchen.  End to end this took about 5 hours including resting time before slicing.  I weighed out all the major ingredients (vs. volume measurements.)

2 cups boiling water, divided

1 cup (142g) Six-Grain Blend

2 cups (454g) 50/50 sourdough starter

1-3/4 cups (198g) white whole wheat flour

1-3/4 cups (205g) bread flour

2-1/2 tsp. salt

2 Tbs. (43g) honey

1-1/2 tsp. yeast

2 Tbs. vegetable oil, plus extra to grease the dough

Put the Six-Grain Blend into the mixing bowl and pour a cup of boiling water over it.  Mix well and let cool to lukewarm.  Then add the sourdough starter and stir.  Then mix in the flours, salt, honey, yeast, and oil.  Mix with a dough whisk until all the flour is moistened.  Cover and allow to sit for 15 minutes to auto-lyse.  Then in a standing mixer using the dough hook, knead the dough until it forms a soft dough.  Coat lightly in oil, cover and allow to rise in a warm space until nearly doubled, about 1 to 1-1/2 hours.

Remove the dough from the bowl and knead a few times to degas it.  Lightly oil a round bread-baking bowl and cover the bottom of the bowl with cornmeal.  Form the dough into a ball and put in in the bread-baking bowl.  Cover with a clean cloth and allow to rise until puffy, about 1 to 1-2 hours.

About half an hour before the bread is done with its second rising, preheat the oven to 425 degrees and put a cast iron frying pan on the bottom shelf of the oven.

When ready to bake, slash a cross into the top of the dough.  Put the dough and the bread-baking cowl in the oven, and pour a cup of boiling water in the cast iron frying pan.  Bake the dough for 40 to 50 minutes until deep brown in color and fully cooked through (190 degrees internal temperature).  When done, remove the bread from the oven and allow it to cool in the bowl for 10 minutes.  Then remove the bread from the bowl and allow it to fully cool on a wire rack before cutting it.