Preheat your oven to 425°F (220°C). Line a baking sheet with parchment paper or lightly oil it to prevent sticking.
Pat the chicken thighs dry with paper towels to ensure crispy skin. Rub each piece with a tablespoon of olive oil, salt, pepper, sage, and thyme, making sure to coat evenly.
Spread the sliced sweet potatoes on the prepared baking sheet. Drizzle with the remaining tablespoon of olive oil, toss gently to coat, then season with salt, pepper, sage, and thyme.
Place the chicken thighs skin-side up among the sweet potatoes, ensuring there's space around each piece for air circulation.
Roast in the preheated oven for about 35-45 minutes, or until the chicken skin is crispy and golden and the sweet potatoes are caramelized and tender when pierced with a fork.
Use tongs to transfer the roasted chicken and sweet potatoes onto a serving platter. Check that the chicken reaches an internal temperature of 165°F (74°C) for safety.
Garnish with fresh herbs if desired, and serve hot, letting the aromas of sage and thyme fill your kitchen.