Pat the short ribs dry with paper towels. Generously season them on all sides with kosher salt and black pepper to ensure a flavorful crust during searing.

Heat the olive oil in a large skillet over medium-high heat. Place the seasoned short ribs in the hot oil, starting with the bone side up, and sear for 1-2 minutes on each side until deeply browned. The ribs will not be cooked through at this point. Once browned, transfer the short ribs to a large crockpot.

In the same skillet used for searing, add the sliced onions, mushrooms, and tomato paste. Stir well to coat the vegetables in the tomato paste and cook over medium heat until the onions are softened, about 3-5 minutes. Add the minced garlic and cook for an additional minute until fragrant.

Increase the heat to high and pour in the beef broth. Stir and scrape the bottom of the pan to loosen the brown bits left from the searing process. Bring the mixture to a boil, then reduce the heat to medium and simmer for 5 minutes, stirring occasionally to allow the flavors to meld. I always make sure to scrape up every bit for maximum flavor in the final sauce.

Pour the hot vegetable and broth mixture over the seared short ribs in the crockpot. Cover with the lid and cook on low for 7-8 hours, or on high for 3-5 hours, until the ribs are tender and easily fall off the bone.

Once the short ribs are done, carefully remove them from the crockpot. Serve the ribs hot, spooning the rich mushroom and onion sauce over the top. These ribs are especially delicious served over mashed potatoes for a hearty meal. For an extra burst of flavor, I sometimes finish with a sprinkle of fresh herbs like parsley.