Preheat the grill to medium-high heat, around 400-425°F.
Scrub potatoes clean, pierce with fork, rub with olive oil and salt, then wrap each in foil.
Grill the wrapped potatoes for 45-60 minutes until they are tender.
In a small saucepan, melt butter over medium heat, then add minced garlic and fresh herbs to make garlic herb butter.
Season beef medallions with olive oil, salt, and pepper.
Sear the beef cubes in a hot cast iron skillet for 2 to 3 minutes per side until browned.
Carefully cut open grilled potatoes lengthwise, fill with sour cream mixed with shredded cheese and chives.
Top the filled potatoes with seared beef bites and drizzle generously with the garlic herb butter before serving.