Grind just a little bit of wheat on the finest grind possible. Put the flour into a large bowl; you will use this as your main bread bowl throughout the baking procedure. Leave the mill attached, you’ll be grinding more flour in a little while.
Stir all the other starter ingredients into the freshly ground flour to make a thick goopy mixture. Cover it lightly with plastic wrap and let it rest for at least 2 hours and up to 16. The longer it rests, the better the flavor in the finished bread – an overnight rise would be perfect.
NEXT DAY, THE BREAD
Grind the rest of the wheat and all the rye. There’s no reason to keep them separate; let the flour fall into the same bowl. Use the finest grind to make the smoothest flour possible.
Stir down the starter with a spoon or a dough whisk, and stir in all the freshly milled whole grain flour, water, yeast, sugar, salt, and two-thirds of the bread flour. The dough will be a loose mess at this point. Let it rest 30 to 45 minutes, to let the flour absorb the water, then stir again. It should be more cohesive and quite a lot smoother.
Knead the dough, adding more flour as necessary, about 20 minutes. The dough will be quite soft, and a bit sticky, which is okay.
Put the dough in a greased bowl, cover with a clean tea towel or plastic wrap, and let it rise at room temperature until doubled in volume: 1 to 2 hours, depending on the weather. If you prefer to defer baking, let the dough rise in the fridge. If your dough has been refrigerated, allow it to come to room temperature before shaping; it’ll warm up and rise at the same time.
Gently knock back the dough, and knead a turn or two on a lightly floured surface. You should notice that the dough is much less sticky, and handles quite easily. Shape into either one round ball or two smaller ones. Put parchment paper on a baking sheet, dust it with cornmeal or semolina, and place the loaf or loaves on top, seam side down. Cover the bread gently with the tea towel or greased plastic wrap, and let it rise until it is puffy and about half again as large; about 90 minutes.
Preheat oven to 475˚F (246˚C). Dust the top of the loaf or loaves with a bit of bread flour, and slash the loaf or loaves with a sharp knife or lame. Place the bread in the middle of the oven.
Bake the bread about 25 to 30 minutes, or until it’s a rich golden brown, and it sounds hollow when thumped. If you use a digital probe thermometer, the interior temperature must register at least 190°F (87˚C). If you’re baking two smaller loaves, they will bake more quickly, so keep your eye on them, and check them at 15 or 20 minutes. When they’re fully baked, they smell wonderful!