One's ultimate foundation or starting point will be circular. That's inescapable, but it's also not necessarily a problem. Let's say that I claim empiricism is my ultimate foundation. You ask "How do you know empiricism is true?" If I say "By logic" then I've made logic my ultimate foundation and not empiricism. That just moves the question to "How do you know your logic is reliable?" if I say empiricism then I've just created a circle. In this case, it's a vicious circle. Most philosophers distinguish between two types of circular arguments: those which are viciously circular and those which are non-viciously circular (or broad circularity).
Only vicious circularity (where the circle is very small) is considered fallacious. For example, the philosopher A. P. Martinich, who as far as I know is not a Christian, has written “if circularity is spread over a great many analyses (the more, the better), it may cease to constitute a defect” (Philosophical Writing, p. 102). The philosophers Julian Baggini and Peter S. Fosl (I know Baggini is an atheist, not sure about Fosl) write: “Are all circular arguments vicious? Not necessarily” (The Philosopher’s Toolkit, 1st ed., p. 78) and they go on to explain that an argument which has premises that can be independently verified is not viciously circular.
Ultimately, every argument or all of our reasoning has broad circularity to it if we try to articulate our entire chain of thought. The only alternative to this is an infinite regress where you never get to any sort of justification. But ideas which are broadly circular can receive a type of justification through a transcendental argument (not to be confused with transcendent). Transcendental arguments (TAs) ask “Given ‘x’ what must be the case?” There is a school of apologetics called Presuppositionalism which specializes in this argument called. It’s discussed in your Five Views on Apologetics book (by John Frame) and happens to be the school of thought that I belong to. But there is a lot more that can be said here (there are Clarkians who call themselves presuppositionalist too, but have important differences and there are two different views of TAs in the presuppositionalist school that I follow (called VanTilian presuppositionalism from its formulator Cornelius Van Til). Here is an example of a TA by a VanTilian presuppositionalist:
http://www.proginosko.com/docs/IfKnowledgeThenGod.pdf but by far the most famous example of a TA being used is this:
The Great Debate: Does God Exist? Bahnsen/Stein -- 1 of 2 Mp3 (the Christian in this debate, Greg Bahnsen, is actually the best debater I’ve ever heard. Even better (far better?) than William Lane Craig in my opinion. Unfortunately, he died in 1995 at the age of 40 while undergoing heart surgery. I don’t agree with all of Bahnsen’s positions, but I’ve never heard anyone who was quicker on their feet than him. At the time of the debate he was relatively unknown and the atheist he was debating, Gordon Stein, was considered the one of the prominent atheists around.)