Preheat oven to 425 degrees F. Line a baking sheet with aluminum foil and place a wire rack on top. Spray the rack with nonstick spray. Set aside. Heat butter in a small saucepan (or the microwave) until just melted. Remove from any heat and then add in garlic cloves, stirring well
Rinse sweet potatoes well with water then pat completely dry with towels. Add to a large bowl and toss with olive oil, garlic butter, salt and pepper. Toss very well to coat. Spread sweet potatoes out in a single layer on the wire rack. Bake for 20 minutes, remove and toss, then bake for 15-20 minutes longer. Sometimes I check within 10 minutes and toss again, and occasionally after the 15-20 minutes, I give them another 5-10 or so. I know using a wire rack can be a pain but it really helps crisp all sides. Try not to crowd the sweet potatoes and if necessary, use a second sheet/rack.
Remove and let cool slightly. Remove the wire rack or place on a large plate and cover in parmesan and fresh herbs, tossing and tossing to coat. If needed, season a bit more too. You can even add some more garlic butter if you wish. Dip in creamy feta!