Step 1: Preheat your oven to 400°F (200°C). Line a large baking sheet with parchment paper for easy cleanup.
Step 2: In a medium bowl, whisk together the honey, soy sauce, 2 tbsp olive oil, Dijon mustard, minced garlic, dried thyme, and red pepper flakes (if using) until well combined. This is your honey-garlic sauce.
Step 3: Add the sirloin cubes to the honey-garlic sauce, tossing to coat thoroughly. Let marinate for at least 10 minutes while you prepare the potatoes, or up to 2 hours in the refrigerator for deeper flavor.
Step 4: In a separate large bowl, combine the quartered potatoes with 1 tbsp olive oil, salt, and black pepper. Toss until the potatoes are evenly coated.
Step 5: Arrange the seasoned potatoes in a single layer on one side of the prepared baking sheet.
Step 6: Place the marinated beef cubes in a single layer on the other side of the baking sheet, ensuring they are not overcrowded. Discard any remaining marinade.
Step 7: Roast for 25-30 minutes, flipping the beef and potatoes halfway through, until the beef is cooked through and the potatoes are tender and golden brown.
Step 8: For extra crispiness, turn on the broiler to high during the last 3-5 minutes of cooking, watching carefully to prevent burning, especially due to the honey.
Step 9: Remove from the oven, garnish with fresh parsley or chives if desired, and serve immediately. Enjoy your effortless one-pan dinner!