Preheat Oven: Preheat your oven to 200°C (400°F). Line a large rimmed baking sheet with parchment paper.
Prep the Potatoes: Wash and scrub the sweet potatoes thoroughly; pat them completely dry.
The Hasselback Cut: Place one sweet potato between two wooden spoons or chopsticks. Use a sharp chef’s knife to make thin slices (about 1/8 inch apart) across the potato. The spoons will stop your knife from cutting all the way through.
Prepare Herb Oil: In a small bowl, whisk together the extra virgin olive oil, minced garlic, dried oregano, thyme, salt, and pepper.
First Brush: Place potatoes on the baking sheet. Use a pastry brush to apply 3/4 of the herb oil mixture over the potatoes, ensuring the oil gets inside the slits.
Bake: Roast for 25 minutes. The slices will begin to fan out as they cook.
Baste for Crispiness: Remove from the oven. Brush the remaining oil over the potatoes and into the open gaps.
Final Roast: Return to the oven for another 20–25 minutes until the centers are tender and the edges are golden brown and crispy.
Garnish and Serve: Remove from the oven. If using feta, sprinkle it over the hot potatoes immediately. Top with fresh parsley and serve warm.