Heat the oven to 375°F. Put 4 tablespoons of the butter into a 2-quart baking dish and place it in the oven for 4–5 minutes to melt while you prep the rice.
Rinse the rice under cool water until it runs mostly clear; drain very well so extra water doesn’t dilute the flavors.
Remove the hot dish and swirl to coat. Add the drained rice and toss to coat every grain in the melted butter.
In a bowl or large measuring cup, whisk together the French onion soup, condensed beef broth, Worcestershire, and pepper until smooth. Pour the mixture over the rice and stir to combine. Cut the remaining 4 tablespoons butter into small pieces and dot them evenly over the top. Cover the dish tightly with heavy-duty foil.
Bake covered for 25 minutes. Stir well from the bottom to redistribute the rice and butter, re-cover, and bake 15 minutes more.
Uncover, stir once more, and bake uncovered for 15–20 minutes, until the liquid is absorbed and the top looks glossy with little bubbling at the edges. Turn off the oven, crack the door, and let the rice rest inside for 5 minutes before fluffing and serving.