Preheat your oven to 360F

Season the short ribs generously with salt and black pepper. Heat the vegetable oil in a large Dutch oven or oven-safe pot over medium-high heat.

Working in batches, sear the short ribs on all sides until they are browned and crispy. This will take about 5 minutes per batch. Remove the ribs from the pot and set them aside.

In the same pot, add the chopped onion, carrots, celery, and garlic. Sauté the vegetables until they are softened and lightly browned, about 5 minutes.

Stir in the tomato paste and cook for an additional 2 minutes to enhance its flavor.

Pour in the red wine and scrape the bottom of the pot to release any browned bits. Allow the wine to simmer for a few minutes until it has reduced slightly.

Add the beef broth, thyme sprigs, and bay leaves to the pot. Return the short ribs to the pot, nestling them into the liquid.

Cover the pot with a lid and transfer it to the preheated oven. Braise the short ribs for about 2.5 hours, or until the meat is tender and falling off the bone.

Once the short ribs are cooked, remove them from the pot and set them aside. Skim any excess fat from the surface of the cooking liquid.

Strain the cooking liquid into a saucepan and simmer it over medium heat until it has reduced.

Serve the short ribs with the braising liquid or sauce, and accompany them with mashed potatoes.