Heat oil in a large case-iron or other heavy-bottomed pot over medium-high heat. Working in batches, add meat and cook until well browned all over, about 5 minutes per batch. Transfer meat to a medium bowl and set aside.

Reduce heat to medium and melt 4 tbsp of the butter in pot. Add onions and cook, stirring occasionally with a wooden spoon, until deep golden brown, 35-40 minutes. Transfer onions to bowl with meat and set aside.

Add the remaining 3 tbsp, butter to pot, then immediately add flour and cook, stirring constantly, until deep golden brown but not burned, about 2 minutes.

Add stock and beer, scraping browned bits stuck to bottom of pot. Return meat , onions, and accumulated juices to pot. Add bay leaves, thyme, sugar, and vinegar and season to taste with salt and pepper.

Reduce heat to medium-low and simmer, partially covered, until meat is very tender and sauce is dark, thick, and velvety, 1-1/2 - 2 hours. Remove and discard bay leaves and thyme before serving.