You might think it would be hard to produce sweet potato fries that are simultaneously burnt and soggy... yet I've managed to perform this feat several times! What am I doing wrong? I coat them in some bacon fat or lard, add a bit of sea salt and paprika and put them in a preheated 350 degree oven. Every time, they burn and go limp rather than getting crisp!
Here is a couple ideas.
Increase your baking temperature. 350 degrees seems really low. Most oven fries recipes call for a temp over 400 degrees.
Make sure the fries are all a uniform size. About 1/2 an inch wide strip are a good size for baking.
Make sure the potatoes are patted dry before you toss them in oil. I would toss them in oil vs lard. Better to have a thin coat of oil on your uniform pieces.
Spread them out over a cookie sheet. No touching! Each fry should have a little space around its borders. Clumping food together can actually cause the food to steam instead of roasting.
Lastly, if you salt, salt at the end of the cooking process. Right when you take them out of the oven.
Try those tips and see if they help. There are a couple other tricks that can help but they require a bit more work.
I use a non primal oxymoron microwave and first slice a hole in the yam or sweet potato--to prevent it from exploding and cook til soft. Then slice 1/4 inch thick while hot and pan fry in butter and coconut oil til golden brown on both sides. It is a great substitute for the hash brown potatos I used to consume in volume.
Sweet potato fries are tricky in that they have a higher moisture content. So you're not going to get the same effect as with regular potatoes.
One option would be to bake them at a low temperature to dry out, and then put them in again at a 350 degree temperature -- sort of like what I used to do with blanching regular fries: blanche them in hot oil at 275, then fry them again at 350.
Another thought is that they might be too close together/crowded. If they are, they're not going to get crisp on you at all. You might have to move them apart from each other, and break up your single batch onto two cookie sheets.
Don't know if you are opposed to frying them...but if not...here's my treat that I enjoy every now and then.
Julienne the sweet potato and fry them in small batches in coconut oil. Crispy and delicious!
Secret to sweet potato fries?
Fry them. ;)
They're called FRIES for a reason.
I personally like a combo of bacon grease/butter/splash of EVOO. Sprinkle with mildly ground Himalayan rocksalt and dip in a home-made Garlic All-i-oli (Real Catalan Mayonnaise made with NO egg yolk :)
P.S. Did you know that Mayonnaise comes from Mahón on the Island of Menorca?
grease the baking sheet with butter, cut them into uniform strips, drizzle melted butter on top, bake at 400 degrees for 30 minutes. No flipping or opening the oven. Remove with a metal spatula and season them afterwards.