The key to buying a country loaf from Tartine is to pre-order it 24-72 hours in advance. They only make a limited amount of bread each day so there's no guarantee for walk-ins. Since loaves come out of the oven around 4:30pm, I went early and ate/bought pretty much everything in the bakery while I waited. My game knows no shame.
I've included some bread nerd notes at the bottom of this post.