Heat a large pot over high heat.

Season flanken with salt and pepper. Add 1/2 teaspoon oil and the flanken to pot and brown about two minutes per side. Remove meat from pot and set aside.

Add remaining oil and onions to pot. Cook for just two minutes, until onions are heated through (since they are already cooked!).

Pour wine into onions and stir, scraping up any bits from the bottom of the pan. Cook for two minutes.

Place flanken into a mesh soup bag (this will make it easier to remove before blending). Return meat to the pot and add potatoes and 12 cups chicken stock. Bring to a boil, reduce heat, and simmer for one to one and a half hours. 

Remove meat and blend soup using an immersion blender. If soup is too thick, add reserved chicken stock 1/2 a cup at a time, until it’s the consistency you like. 

Return meat to soup. Continue to cook soup on low heat, stirring often, until meat is tender.

Once tender, remove meat, shred with a fork, and then return to the pot. Serve soup hot and enjoy!