In a small bowl, mash together the garlic, salt and rosemary into a thick paste. Add olive oil, incorporating it into the paste. Set aside.
Make sure the sweet potatoes are sufficiently washed and scrubbed. Slice each sweet potato lengthwise into 1/2 inch pieces. Stack these pieces together, and cut lengthwise again, to form 1/2 inch strips.
In a large bowl, toss the potato strips with the prepared garlic, salt, rosemary and olive oil paste.
Spread the potatoes out on a baking sheet that is either lined with parchment paper or lightly coated in olive oil.
Roast potatoes for 30-35 minutes, checking every ten minutes and rotating the pan for even browning.