In a large skillet over medium heat, add the olive oil and 1 tablespoon of butter. Once the butter has melted, add the sliced onions. Cook, stirring occasionally, for about 20-30 minutes or until the onions are caramelized and golden brown. Remove from heat and set aside.

While the onions are caramelizing, season the Tomahawk steak generously with kosher salt, crushed white peppercorns, garlic powder, and smoked paprika on both sides. Let it sit at room temperature for about 30 minutes.

Preheat a grill or cast-iron skillet over high heat. Once hot, sear the Tomahawk steak for 4-5 minutes on each side to develop a nice crust. Reduce the heat to medium and continue cooking to your desired doneness (about 15-20 minutes for medium-rare), using a meat thermometer to check the internal temperature (130°F for medium-rare).

In a separate saucepan over medium heat, melt the remaining 4 tablespoons of unsalted butter. Add the sage leaves and cook until the butter is golden brown and the sage is crispy, about 3-4 minutes. Carefully pour in the beef broth and bring to a simmer. Cook for an additional 5 minutes to allow the flavors to meld. Season with freshly ground black pepper to taste.

Once the steak is cooked to your liking, remove it from the grill or skillet and let it rest for at least 10 minutes. This allows the juices to redistribute.

Slice the Tomahawk steak and top with the caramelized onions. Drizzle the brown butter sage jus over the top. Serve with your choice of sides.