Garlic Butter Steak and Potatoes Skillet

Herb Sauce:
• Zest and juice of 1 lemon
• ¼ cup finely chopped fresh parsley
• 2 tablespoons finely chopped fresh mint
• 1 garlic clove, smashed
• Salt and freshly ground black pepper
• A pinch of red-pepper flakes
• 2 tablespoons extra-virgin olive oil