Believe it or not there's no baking involved in this unctuous and impossibly good meatloaf.
Heat 2 teaspoons oil and caramelize the onions in a large skillet over low heat until they are completely golden, stirring frequently. Season with salt and pepper. Set aside to cool.2.
Preheat the oven to 325°F. Season the short ribs with salt and pepper. Heat 1 tablespoon of the oil in a large pot or Dutch oven. Sear the ribs in batches on all sides. Add the stock and caramelized onions, cover, and braise in the oven until ribs are very tender, approximately 5 to 6 hours. Remove the pot from the oven and let the ribs cool in the juices.3.
When cool enough to handle, transfer the ribs to a cutting board. Strain the braising liquid, setting the onions aside, and reduce the liquid by half over medium heat.4.
Remove the bones from the ribs (if there are bones), and shred the meat, including any fat that remains. Place the meat in a large bowl. Add 1 cup of the braising liquid and the reserved onions to the meat and toss to blend well. Taste and adjust the seasoning with salt and pepper. Pack the mixture into an 8 x 8-inch pan, top with parchment, and press another pan on top bottom-side down. Compress the top pan with 4 or 5 large cans. Set it all on a baking sheet to collect any juices. Refrigerate overnight or for up to 48 hours for best results.5.
Run a knife around the edge of the meatloaf pan and heat the bottom briefly (15 to 20 seconds) over the stove to release the meat. Turn the pan upside-down to release the loaf. Slice it into 2 x 2-inch squares.6.
For each serving, heat a cast-iron pan over medium-high heat. Sear each meatloaf square on both sides and transfer them to a 350°F oven for 5 to 10 minutes to heat through.