Atheists often make the extraordinary claim that "extraordinary claims require extraordinary evidence". This statement is highly flawed, for a number of reasons, many of which have been addressed by this ministry. See, for example, here, here, and here. Ultimately, the very existence of this extraordinary claim is evidence of the extraordinary mindset behind atheism. In all scenarios, ordinary evidence is sufficient for the ordinary mind.
But the word "extraordinary" doesn't necessarily mean excessive. Rather, it means something along the lines of "beyond the ordinary". Ordinary evidence would be the use of things like corroborating secular record. The New Testament tells us Jesus was crucified, Tacitus records that Jesus was crucified, there's a little bit of evidence. Of course, we don't just rest our case there, but that's just a taste of what "ordinary" evidence would be.
But extraordinary evidence would be something that one wouldn't normally argue from. For example, the use of a fallacious argument in a non-fallacious way. This would be extraordinary, because usually a fallacy is, of course, fallacious. It renders an argument invalid. Now, consider this: Of all the fallacies in the world, circular reasoning is the most well known. Even without knowing the word "fallacy", you know by instinct that circular reasoning doesn't work. But there is one situation in which it has to.
Tell me, how do you know that you can reason? In order to argue for your reasoning abilities, you must first assume you possess them. You must use your reasoning abilities in order to know that you have them. This is circular, ultimately boiling down to "I know I can reason because I know I can reason". Thus, in this extraordinary case, circular reasoning cannot be a fallacy. If it was, we couldn't even know we could reason.
This leaves us with a dilemma. If we don't know if we can reason, we can't really reason about anything. From allegedly "extraordinary" claims like the resurrection of Christ, right the way to every day claims like "the paint is wet", we cannot assess truth unless we can reason. Now, we could just say "I can reason" anyway. But tell me, are we not also fallible? How many times have you been wrong in your life? Even as a reasonable being, you are hardly worthy as a foundation for reason.
But God is.
See, God, specifically the God of the Bible, is omniscient (i.e. He knows all truths, actual and potential), and omnipotent (i.e. He is capable of fulfilling all His purposes). The Bible also tells us He made us with the intention that we reason.
Now, if this is true, we have reason to believe we can reason. This may be circular, but so is every other argument you could bring forth for our reasoning abilities. The difference is, this is the superior circle in every conceivable way. Our reasoning abilities tell us that we are also fallible, and not even all equally capable of reason, and so we are an invalid source for our own reasoning ability. In atheistic philosophies, truth might not even be universal or immutable, and if it is, we have no reason to believe we can pursue it. Even other gods do not provide the same solid foundation as God does, for they often demand we forego our reasoning abilities. Only the God described in Scripture provides a solid foundation for the very reasoning abilities we must assume we have in order to discuss His existence.
Thus, the extraordinary evidence for Christianity is that it is the one and only faith that can be reasonably defended by circular reasoning. Ordinarily, circular reasoning would be a fallacy, but at the deepest level of philosophy, it cannot be. This, therefore, is very extraordinary. When we ask "can I reason", the answer we get is "yes, the fear of the Lord is the beginning of wisdom". God leads to reason, reason leads to God, God leads back to reason, reason leads back to God. Thus, your extraordinary evidence for Christianity is simply that you are able to have this discussion, but you can only know that if you accept the Christian faith. All other faiths, including many corruptions of the Christian faith, inevitably fail to account for our reasoning abilities, and in many cases even call them into question.