Update 2:
On the last day of our trip, we attempted a quad x bang. (What a terrible idea in the end!) 
Tartine Bakery (Revisit)
Even though we arrived a few minutes after they opened, they had very few items for sale, which seemed odd. We really enjoyed the Almond Croissant from our last visit, but like our first visit’s plain Croissant, this time, the entire batch of Almond Croissants was partially burnt(!). 
(As in black char on top.)
We asked the server about that (they had just opened), and he looked down, as if noticing them for the first time. He blurted out, “Oh yah… they do look burnt. Sorry, that’s all we have right now.” 
So we skipped that and went on to…
Croissant:
Time from Oven: 15 minutes.
This time, the plain Croissant wasn’t burnt on top (they seem so inconsistent), and it had a light crispness and some good butteriness. This was probably the best rendition of Croissant we’ve had at Tartine to date. 
Lemon Poppy Tea Cake:
Their Lemon Poppy Tea Cake was wonderful. Moist, yet crumbly, dense enough to be like a good Pound Cake, but with some delicate Lemony sweetness.
Tartine Bakery
600 Guerrero St.
San Francisco, CA 94110
Tel: (415) 487-2600
Arsicault Bakery
We arrived at Arsicault next, home of our favorite Croissant in SF. We couldn’t wait to try it again (and there was a line out the door).
Croissant:
Time from Oven: 15 minutes.
Flaky, crisp, so airy inside, with a deep Butter flavor. It still remains our favorite Croissant in San Francisco! 
SO GOOD! 
We bumped into Baker-Owner Armando Lacayo who was chatting it up with all the customers. He seemed so jovial and friendly.
He mentioned he was going to try opening up a Sandwich shop (baking their own Bread(!)) soon, which sounds like an awesome place to visit on our next trip. Hopefully it’s as good to Sandwiches as Arsicault is to Croissants. 
Thank you again @ipsedixit for the great rec!
Arsicault Bakery
397 Arguello Blvd.
San Francisco, CA 94118
Tel: (415) 750-9460
This was a great start to our morning already. But our quad x bang continued on… (next thread)