Place steak, 6 Tbsp. olive oil, sliced garlic and parsley in a resealable plastic bag, and rub ingredients into steak. Let marinate 1 hour at room temperature or overnight in refrigerator.

Preheat oven to 450°F. In a large bowl, toss potatoes with remaining 2 Tbsp. olive oil and crushed garlic; season with salt and pepper. Spread potatoes on an oiled baking sheet and roast until golden brown and crisp, about 20 minutes, turning occasionally with a metal spatula.

Remove steak from marinade, rubbing off any garlic pieces. Season with salt and pepper. Heat a grill pan over medium-high heat. When hot, brush with oil, add steak and cook for about 7 minutes. Turn and cook for 7 minutes on other side for medium-rare. Transfer steak to a plate, tent with foil to keep warm and let rest for 10 minutes.