The Sandwich: Jambon/Fromage
Tracking down a sandwich is my mission, this one in Paris, and made by the Martin family in the 10th arrondissement. By tracking down the ingredients for one sandwich, made by one shop, makes the task of understanding how Paris gets fed manageable, although still confusing and complicated. Ingredients for one food item at one location often change from one day to another; bakers buy their yeast from the best supplier at the most reasonable cost, for example. 
The vagaries of supply chain dynamics means that you can’t track down all ingredients for all sandwiches made by one baker, but simply one made at one time on one day. Thus the challenge. And the opportunity.
So the tracking began today and thankfully, our bakers were all in, happy to share their shop, ovens, and interest in the adventure. They hauled out flour sacks, tubs of salt and yeast, and labels from packaged ham and cheese. Yes, Emmental. Next step: find those supply chain delivery trucks, the ham processor, cheesemaker, and yes, the cows and pigs.