Preheat your oven to 300°F (150°C).
In a small bowl, combine the smoked paprika, garlic powder, onion powder, sea salt, and black pepper to create a dry rub.
Rub the spice mixture evenly over all sides of the beef brisket, pressing it into the meat.
Heat a heavy oven-safe skillet over medium-high heat and sear the brisket for 2-3 minutes per side until a dark crust forms.
Cover the skillet tightly with a lid or heavy-duty foil and transfer it to the oven to roast for 3-4 hours until the meat is fork-tender.
While the meat rests, heat the olive oil in a separate non-stick pan over medium-low heat.
Add the thinly sliced yellow onion and cook slowly, stirring occasionally, for about 20 minutes until they are deeply caramelized and golden.
Stir in the apple cider vinegar to deglaze the pan, scraping up any flavorful browned bits from the bottom.
Steam the broccoli florets in a steamer basket for 5-6 minutes until they are vibrant green and tender-crisp.
Slice the rested brisket against the grain and serve it topped with the caramelized onions alongside the steamed broccoli.