I had a great success in sourdough this week, with the most impossibly light and even crumb.
My previous sourdough, and many photos I've seen of quality sourdough, have a preponderance of large irregular bubbles. This is totally unlike that.
The recipe is Flo's 1.2.3 proportion:
400g warm water
600g flour (about 1/3 whole wheat, the rest white AP)
12g salt (about 2 teaspoons table salt)
The levain, assembled the night before, is simply a freshly fed starter: 70g mature starter, 70g water, 70g flour, mixed in a smallish bowl, and folded with a spoon a few times before bed.
Day of, combine the levain, water, and flour; stir just to moisten, then sprinkle with the salt (so I don't forget, and to let it start to absorb) - the autolyse. I think I left it for an hour. Knead with the stand mixer for say six minutes. Rest for an hour, stretch and fold in thirds a couple times, then long rise in the "easy bake oven" (oven with the light bulb turned on) until it doubled, which happened surprisingly fast, in less than 3 hours.
I shaped it into 4 nice mini-loaves of French-style bread. Vertical slices are a good size for French toast or just everyday bread/toast, plus you get more heels, a perfect size for sandwiches when sliced horizontally.
Anyhow, after a faster-than-usual final proofing, I finished them in a 450F oven with a pan of water, and liberal spray-bottle for steam and crust.
As noted, I was blown away by how perfectly even and fine the crumb is. The whole wheat flour surely plays a role here, but it's no change from how I've usually baked this bread. I didn't use any bread flour except a couple tablespoons left over in the starter.
The biggest change from my previous sourdoughs is how long I kneaded with the stand mixer. Normally I don't do this, instead mixing by hand and doing only a few stretch-and-folds. The more intense kneading at the beginning distributes the colony and its proto-bubbles more consistently, while stretch-and-fold I guess would result in more distinct layers of more-or-less active cultures, and pockets of larger or smaller bubbles as a result.
Flo's formula is great; easy to remember, easy to scale, and flexible on assembly and fermentation times. When I built this one, I did a sort of "mise en place" with the bowl of levain, a measuring cup of water, and a tub of pre-mixed flours, so I could simply combine them the next morning.