Preparing French Onion Steak Pinwheels is simple when you follow these clear steps:

1. Caramelize Onions: In a large skillet, heat olive oil and butter over medium heat. Add sliced onions, salt, and pepper. Cook, stirring occasionally, until onions are golden brown and caramelized (about 15-20 minutes).
2. Season the Steak: Lay the flank steak on a cutting board. Use a meat mallet to pound the meat to an even thickness, about 1/2 inch. Season both sides with garlic powder, thyme, salt, and black pepper.
3. Prepare Filling: Once the onions are caramelized, remove them from heat. Stir in half of the shredded Swiss cheese until melted and combined with the onions.
4. Assemble Pinwheels: Spread the onion-cheese mixture evenly over the flank steak. Roll the steak tightly from one end to the other, ensuring the filling remains inside.
5. Secure the Roll: Use cooking twine or toothpicks to secure the rolled steak at several intervals to keep it intact during cooking.
6. Sear the Pinwheels: In the same skillet, add a bit more oil if necessary, and sear the steak pinwheels over medium-high heat for about 3-5 minutes on each side until browned.
7. Bake: Preheat your oven to 350°F (175°C). Transfer the pinwheels to a baking dish. Pour the beef broth around the pinwheels for added moisture. Bake for 20-25 minutes until cooked through and cheese is bubbling.
8. Rest the Pinwheels: Remove from the oven and let the pinwheels rest for 10-15 minutes before slicing.
9. Slice: Carefully remove twine or toothpicks, and slice the pinwheel roll into 1-inch thick slices.
10. Garnish and Serve: Top with the remaining Swiss cheese and any leftover caramelized onions if desired.

These straightforward instructions will ensure that your French Onion Steak Pinwheels turn out perfectly every time!