Preheat oven to 300°F(149°C).
Sear the ribs: Season short ribs on all sides with kosher salt and black pepper. Heat 2-3 tablespoons of avocado oil in a large Dutch oven over medium-high heat. Sear the short ribs on all sides until golden brown. Work in batches if needed. Transfer to a roasting pan.
Caramelize the vegetables: Remove excess fat, leaving about 1-2 tablespoon in the pan. Add onions, carrots, celery, and garlic. cook for 10 minutes, stirring often, then add tomato paste and cook for 5 more minutes to caramelize.
Deglaze: Pour in the red wine, scraping up all the browned bits from the bottom. Simmer until reduced by half.
Braise: Add caramelized vegetables, herbs (bay leaves, thyme, rosemary), peppercorns, and enough veal stock to come halfway up the sides of the ribs.
Bake low and slow: Cover the ribs with parchment paper and foil, then braise in a 300°F (149°C) oven for 3 hours, until the meat is fall-apart tender.
Make the sauce: Remove the herbs and blend the braising liquid and vegetables in a blender until smooth. Alternatively, you can drizzle Demi-Glace over top the short ribs.
Serve: Let rest 10 minutes, then serve with mashed potatoes, creamy polenta, or roasted carrots. Spoon sauce over the top and enjoy.