Pat 2½ lbs. beef short ribs dry if necessary. Finely dice 1 onion, 8 celery ribs, and 3 medium carrots.
Season all over with salt and pepper. Pat the seasoning into the meat.
Warm half of your vegetable oil in a skillet over medium-high heat and sear the short ribs on all sides, in two batches so you don't overcrowd the skillet. Make sure to sear until you have a nice mahogany crust.
Add the onion, celery, and carrots to the skillet along with the remaining oil. Reduce the heat slightly so the vegetables don't burn.
Cook the vegetables for a couple minutes, then add 1 clove minced garlic. Cook a minute more, then add ½ cup red wine to deglaze the pan. Scrape up brown bits from the bottom of the skillet.
As it starts to simmer, add 2 Tbsp. balsamic vinegar, 2 Tbsp. tomato paste, ¾ beef broth, ½ tsp. rosemary, and 3 bay leaves. Add the short ribs to the slow cooker.Bring the vegetable mixture to a simmer then pour over the short ribs.
Turn the slow cooker on low and cook for 6 - 8 hours. Remove the bay leaves when it is done and discard them. Serve over mashed potatoes, rice, or thick pasta like pappardelle.
I used bone in short ribs for this recipe but boneless short ribs also work well.
Make sure to give the short ribs a good amount of seasoning with salt and pepper to intensify the flavor.
Important step: Heating oil in a skillet and searing the ribs on all sides in batches so you don't overcrowd the pan. This step is key to beautiful and flavorful short ribs.
You can also use large pieces of carrots and serve them as your side dish.