Preheat your oven to 300°F (150°C).
In a small bowl, combine the smoked paprika, garlic powder, sea salt, and black pepper to create a dry rub.
Pat the brisket dry with paper towels and rub the spice mixture thoroughly into all sides of the meat.
Heat the olive oil in a heavy, oven-safe skillet or Dutch oven over medium-high heat.
Sear the brisket for 3 to 4 minutes per side until a deep brown crust has formed, then remove it from the pan and set aside.
Add the sliced yellow onions to the same pan and sauté for about 5 minutes until they soften and begin to brown.
Pour in the beef broth and apple cider vinegar, using a wooden spoon to scrape up any flavorful browned bits from the bottom of the pan.
Return the brisket to the skillet, nestling it into the onions, and cover the pan tightly with a lid or heavy-duty foil.
Transfer to the oven and braise for 3 hours, or until the beef is tender enough to pull apart with a fork.
Let the meat rest for 10 minutes before slicing against the grain and serving with the jammy caramelized onions and pan juices.