Step 1: Preheat the Oven

1. Preheat your oven to 400°F (200°C). Line a baking sheet with parchment paper or lightly grease it with olive oil.

Step 2: Prepare the Sweet Potatoes

1. Place a sweet potato on a cutting board. Using a sharp knife, make thin, even slices across the potato, about 1/8 to 1/4 inch apart, stopping just before you cut all the way through. The potato should stay intact at the base.
2. Tip: To make slicing easier, place chopsticks or wooden spoons on either side of the potato to act as a guide and prevent you from cutting through completely.
3. Repeat with the remaining sweet potatoes.

Step 3: Season the Sweet Potatoes

1. In a small bowl, combine the melted butter and olive oil. Brush the mixture generously over the tops and into the slices of each sweet potato, ensuring that the oil and butter seep between each cut for even flavor.
2. Season the potatoes with salt and black pepper to taste.

Step 4: Bake the Sweet Potatoes

1. Place the sweet potatoes on the prepared baking sheet. Cover them loosely with aluminum foil to prevent excessive browning at the start of baking.
2. Bake in the preheated oven for 30 minutes, then remove the foil and bake for an additional 20-30 minutes, or until the potatoes are tender in the center and the edges are crisp.

Step 5: Prepare the Maple Pecan Glaze

1. While the potatoes are baking, make the glaze. In a small saucepan over low heat, combine the maple syrup, brown sugar (if using), cinnamon, nutmeg, and salt. Stir until the sugar is dissolved and the mixture is warmed.
2. Add the chopped pecans and cook for an additional 2-3 minutes, stirring occasionally, until the pecans are slightly toasted and fragrant.

Step 6: Glaze the Sweet Potatoes

1. Remove the sweet potatoes from the oven and brush them generously with the maple pecan glaze, making sure to get some glaze between the slices for extra flavor.
2. Return the potatoes to the oven and bake for another 10 minutes, or until the glaze is caramelized and the pecans are toasted.

Step 7: Garnish and Serve

1. Remove the sweet potatoes from the oven and let them cool for a few minutes. Garnish with fresh rosemary or thyme sprigs, extra chopped pecans, and an additional drizzle of maple syrup if desired.
2. Serve the Hasselback Sweet Potatoes warm, and enjoy the delicious combination of flavors and textures.