Preheat the oven to 220°C | 425 degrees F. Line a baking tray/sheet with aluminum foil; set aside.
Wash and scrub the sweet potatoes; pat them dry with paper towel. Carefully slice each sweet potato 1/8-inch slits (or slices) along the tops, stopping 1/2-inch from the bottom (1-cm). Be careful not to apply too much pressure or you may cut straight through.
Prepare the Garlic Butter using this recipe. Melt the butter; mix the lemon juice, thyme, rosemary, salt and pepper (to taste) through the butter. Set aside.
The quicker version:
Wrap each sweet potato in one sheet of paper towel; place on a microwave safe dish and microwave on high setting for 8-10 minutes, or until semi-soft. Brush the butter all over the potatoes and in between the slices; transfer them onto the baking sheet and place in the oven for a further 10 minutes to allow them to continue roasting and crisp up.
The slow version:
Place potatoes onto the lined baking tray/sheet; brush with half of the butter and roast until the center of the potatoes are beginning to soften (30 minutes). Remove from oven, brush with the remaining butter and fan the wedges out lightly with a fork to open up the slices. Return to oven and continue baking for a further 30 minutes, or until soft and tender in the centre and crispy on the outside.