Sua panela não está arruinada. YAY! O que aconteceu é que você queimou a maior parte do tempero. Qualquer outro tipo de panela seria arruinado, mas sua panela de ferro fundido só precisa ser removida e preparada novamente. Se você tiver um ciclo de forno autolimpante, essa é uma ótima maneira de remover completamente a panela. Você também pode jogá-lo em um fogo quente (como uma lareira, fogão a lenha ou fogueira se você tiver um) e apenas deixá-lo até que o fogo está fora e você pode tocar na panela. Para qualquer um desses métodos, a panorâmica deve ser invertida.
Outra coisa que você pode usar para chegar ao metal puro é o limpador de forno, em forno quente ou não, dependendo do produto. Mais uma vez, a panela deve estar virada para baixo.
Complete a missão com lã de aço e detergente, um SOS pad seria ótimo para isso. 
Agora está nu e precisa ser experiente. Infelizmente, vai ficar muito difícil até que você tenha uma boa temporada sólida. Tempere-o algumas vezes e cozinhe apenas alimentos gordurosos por um tempo. Ele voltará eventualmente.
Você pode obter respostas que dizem que você não precisa tirar o tempero que sobrou. Eu discordaria disso, o tempero sobre o tempero mal danificado nunca fica tão strong e suave. Comece do zero.
Procure aqui conselhos sobre temperos: O que é a melhor maneira de temperar uma frigideira de ferro fundido?
Recentemente eu me tornei um convertido de linhaça, então meu método preferido é esse, de -cast-iron / "> Sheryl's Blog , que eu vi pela primeira vez graças à resposta de Neil G para a questão acima do Conselho Temperado. Vale a pena ler todo o artigo, mas aqui estão as instruções dela para temperar a partir do zero. Eu só fiz isso com uma das panelas de ferro fundido que eu herdei da minha avó. O resultado foi fabuloso.The Recipe for Perfect Cast Iron Seasoning
The basic idea is this: Smear a food-grade drying oil onto a cast iron pan, and then bake it above the oil’s smoke point. This will initiate the release of free radicals and polymerization. The more drying the oil, the harder the polymer. So start with the right oil.
Go to your local health food store or organic grocery and buy a bottle of flaxseed oil. It’s sold as an omega-3 supplement and it’s in the refrigeration section because it goes rancid so easily. Check the expiration date to make sure it’s not already rancid. Buy an organic flaxseed oil. You don’t want to burn toxic chemicals into your cookware to leach out forever more. It’s a fairly expensive oil. I paid $17 for a 17 ounce bottle of cold-pressed, unrefined, organic flaxseed oil. As it says on the bottle, shake it before you use it.
Strip your pan down to the iron using the techniques I describe in my popover post. Heat the pan in a 200°F oven to be sure it’s bone dry and to open the pores of the iron a little. Then put it on a paper towel, pour a little flaxseed oil on it (don’t forget to shake the bottle), and rub the oil all over the pan with your hands, making sure to get into every nook and cranny. Your hands and the pan will be nice and oily.
Now rub it all off. Yup – all. All. Rub it off with paper towels or a cotton cloth until it looks like there is nothing left on the surface. There actually is oil left on the surface, it’s just very thin. The pan should look dry, not glistening with oil. Put the pan upside down in a cold oven. Most instructions say to put aluminum foil under it to catch any drips, but if your oil coating is as thin as it should be, there won’t be any drips.
Turn the oven to a baking temperature of 500°F (or as high as your oven goes – mine only goes to 450°F) and let the pan preheat with the oven. When it reaches temperature, set the timer for an hour. After an hour, turn off the oven but do not open the oven door. Let it cool off with the pan inside for two hours, at which point it’s cool enough to handle.
The pan will come out of the oven a little darker, but matte in texture – not the semi-gloss you’re aiming for. It needs more coats. In fact, it needs at least six coats. So again rub on the oil, wipe it off, put it in the cold oven, let it preheat, bake for an hour, and let it cool in the oven for two hours. The picture above was taken after six coats of seasoning. At that point it starts to develop a bit of a sheen and the pan is ready for use.
If you try this, you will be tempted to use a thicker coat of oil to speed up the process. Don’t do it. It just gets you an uneven surface – or worse, baked on drips. Been there, done that. You can’t speed up the process. If you try, you’ll mess up the pan and have to start over.
The reason for the very hot oven is to be sure the temperature is above the oil’s smoke point, and to maximally accelerate the release of free radicals. Unrefined flaxseed oil actually has the lowest smoke point of any oil (see this table). But the higher the temperature the more it will smoke, and that’s good for seasoning (though bad for eating – do not let oils smoke during cooking).
I mentioned earlier there’s a myth floating around that vegetable oils leave a sticky residue. If the pan comes out of the oven sticky, the cause is one of three things:
You put the oil on too thick. Your oven temperature was too low. Your baking time was too short.
It’s possible to use a suboptimal oil for seasoning, like Crisco or bacon drippings, and still end up with a usable pan. Many (most) people do this. But the seasoning will be relatively soft, not as nonstick, and will tend to wear off. If you want the hardest, slickest seasoning possible, use the right oil: flaxseed oil.