Success!

I baked one of the two loaves last night, and the other this morning. They both turned out much better than I expected - they were downright delicious! The exterior is crisp, crunchy, chewy. The crumb is moist and mildly sour like a classic sourdough. It tastes so different than a bread made with active dry yeast - and the baking method (20 minutes in covered dutch oven, then 20 minutes uncovered) produces such a gorgeous exterior! With butter it is heavenly. Like real bread - from a bakery!

loaf #1 in cast-iron dutch oven - you can see that
I scored a square pattern on the top of the dough, but not very
deeply so only  a thin square rose above the rest of the bread

loaf #1, the crumb

loaf #2 cooling - I scored the square more deeply this time,
and for whatever reason this loaf was a bit more flexible
than the first and expanded a bit more