Preheat your oven to 400 degrees Fahrenheit and line a baking sheet with parchment paper.
Dice the Yukon Gold potatoes into one-inch cubes and place them in a large mixing bowl.
Toss the potatoes with olive oil, minced garlic, chopped rosemary, thyme, sea salt, and black pepper until evenly coated.
Spread the potatoes in a single layer on the prepared baking sheet and roast for 25 minutes until golden and tender.
Place the duck leg skin-side down in a cold cast-iron skillet and turn the heat to medium.
Render the fat for 8 to 10 minutes without moving the leg until the skin is deeply browned and crispy.
Flip the duck leg and cook for an additional 3 minutes to warm through, then remove from the pan and let rest.
In the same skillet using the residual duck fat, quickly sauté the asparagus for 4 minutes until vibrant green and tender-crisp.
Plate the crispy duck leg alongside the herb-roasted potatoes and sautéed asparagus.