Mix the yeast and salt with the water in a large bowl. Set aside.
Mix the flours, without kneading, into a heavy duty stand mixer with the dough hook attached. Pour wet ingredients into dry ingredients and knead with dough hook until a soft and smooth dough forms and pulls away from the sides of the bowl, about 6 minutes (here is where the extra tbsp of oat flour may come in, depending on how sticky your dough is).
Place kneaded dough in a lightly greased bowl and cover and let rise until doubled, about 2 hours. The dough can be used immediately after the initial rise, though it is easier to handle when cold. Refrigerate in a lidded container and use over the next 10 days.
On baking day, lightly grease a 9 x 5-inch loaf pan. Dust the surface of the refrigerated dough with flour and cut off a 1 1/2-lb. (cantaloupe-size) piece. Dust the piece with more flour and shape it into a ball. Drop into the loaf pan. all to rest and rise for 1 hour and 40 minutes (or just 40 minutes if you're using fresh, unrefrigerated dough).
Twenty minutes before baking, preheat the oven to 400 degrees F, with an empty broiler tray on a shelf below the bread. Place the loaf on a rack near the center of the oven and just above the broiler pan. Pour 1 cup of hot tap water into the broiler tray and quickly close the oven door. Bake for 45 minutes or until deeply browned and firm. Allow to cool before slicing or eating.