Remove the rump roast from the refrigerator about 2 hours (no longer than that) before starting recipe to allow it to come closer to room temperature.

Use a sharp, thin knife to make three slits about 2 to 3 inches deep on one side of the roast. Stuff each slit with one garlic clove and some sea salt and black pepper. Flip the roast over, and make three more slits on the other side, and stuff with garlic, sea salt, and black pepper. Rub the remaining sea salt and pepper over the outside of the roast.

Preheat oven to 275 F.

Melt the salted butter over medium-high heat in an oven-safe skillet. Sear all sides of beef to brown. This should take about 15 minutes. Remove roast to a plate, and de-glaze the pan with the beef broth and dry red wine.

Place the roast back in pan, and place onion slices and rosemary sprigs around it.

Roast at 275 F until you get an internal temperature of 115 F, which should take about 12 to 15 minutes per pound of meat (48 minutes to 1 hour for 4 pounds).

Remove the roast to a cutting board, tent loosely with foil, and allow it to rest for about 20 minutes. Serve when the internal temperature reaches 130 F for medium-rare or 125 F for rare.