So there were 4 things that could have contributed:
1) Pre-hydrating the flour, even just for a little while.
2) A really active levain compared to the first one.
3) A single stretch and fold after fermenting cold overnight.
4) A ten or eleven hour, warmer ferment for the final proving.
Stupidly good, tasty bread and a big enough loaf that I get my sandwiches out of it today! :party:
Chuffed. Now I need reading material...
Have you been on either The Fresh Loaf or sourdough.com?