Season beef short ribs with salt and black pepper.
Heat olive oil in a large Dutch oven over medium-high heat.
Sear short ribs on all sides until deeply browned, then remove and set aside.
Add sliced onions to the same pot and cook over medium heat.
Stir onions frequently and caramelize for 30 minutes until golden brown.
Add minced garlic and tomato paste and cook briefly.
Deglaze the pot with white wine and scrape up browned bits.
Return short ribs to the pot and add beef broth, thyme, and bay leaf.
Bring to a boil, then reduce heat to low and cover.
Simmer gently for 2 hours until meat is tender.
Remove bones, shred beef, and return meat to the soup.
Taste, adjust seasoning, garnish with parsley, and serve hot.