baked sweet potato fries

I've been on a search for a good technique for making delicious baked sweet potato fries. When I make them they are never crispy enough. I usually cut 2 large sweet potatoes into 1/4/-1/2 inch fries coat them in 2 TBSP olive oil and the desired spices and bake for 30 minutes. They're always fine, but not sufficiently delicious. I'd love to get a better recipe. I often wonder if the problem is our oven.