In a large bowl or zip-top bag, combine the lean beef with soy sauce, neutral oil, Worcestershire sauce, brown sugar, diced yellow onion, minced garlic, kosher salt, black pepper, and crushed red pepper flakes. Ensure the beef is coated evenly, then seal the bag or cover the bowl. Refrigerate for at least 6 hours or overnight.

Bring a large pot of salted water to a boil. Carefully add the small red new potatoes and cook for about 7 minutes, just until slightly tender but still firm to the bite. Drain the potatoes and let them cool for a few minutes before towel drying.

In a small bowl, mix together the softened unsalted butter, minced Italian parsley, black pepper, and a sprinkle of salt. Blend until well combined.

Once the beef has marinated and the potatoes are cool, thread the marinated beef chunks and par-cooked potatoes alternately onto skewers.

Preheat your grill to medium-high heat. Place the assembled skewers on the grill and cook for about 10 minutes, turning occasionally.

Remove the skewers from the grill and let them rest for a few minutes. Serve hot with additional parsley butter on the side.