PBW works better at higher temps. You can make your own homemade version for around $3 a pound.
If the elements aren't stainless there's a black coating on them. BKF may remove that. Some but not all elements can be fired dry, that would burn off the cake too, but it creates nasty smoke.
Really, soaking/immersing or slow simmering in a hot lye solution (1% lye is probably strong enough) should take care of it. Ace Hardware sells gallon jugs of 17% lye solution for ~$2. Or a teaspoon of drain opener in a gallon of water.
Lye is dangerous, be very careful! It's caustic, it dissolves skin and can (will) cause blindness if you get it in your eye if left unrinsed properly and untreated by a professional ASAP. Wear goggles or a full face shield and protective gloves. Not kidding.