Preheat oven and prepare baking sheet: Position an oven rack in the center and preheat oven to 400°F (200°C). Line a large rimmed commercial baking sheet with parchment paper or heavy-duty foil lightly brushed with oil.

Mix seasoning marinade: In a small bowl, whisk together 2 tablespoons olive oil, fresh lemon juice, minced garlic, chopped rosemary, onion powder, paprika, dried oregano, kosher salt, and black pepper.

Season potatoes: In a medium bowl, toss the halved baby potatoes with the remaining 1 tablespoon olive oil and a pinch of salt and pepper. Spread the potatoes evenly onto the prepared baking sheet, turning cut-sides down for maximum caramelization.

Season chicken thighs: Pat chicken thighs thoroughly dry with paper towels (dry skin guarantees ultra-crisp results). Rub the garlic-rosemary marinade all over the chicken, making sure to get underneath and on top of the skin.

Arrange on sheet pan: Nest the seasoned chicken thighs skin-side up amongst the baby potatoes. Scatter lemon rounds and whole fresh rosemary sprigs across the tray between the chicken pieces.

Roast to golden perfection: Roast in the preheated oven for 38 to 42 minutes, or until the chicken thighs reach an internal temperature of 175°F (80°C) with crisp golden crackling skin and the potatoes are deeply caramelized and fork-tender.

Rest and serve: Remove from oven and let rest for 5 minutes. Spoon the savory pan drippings over the chicken and potatoes, garnish with fresh rosemary, and serve immediately with charred lemon wedges!