Looking for a good source for using 2D Fast Fourier Transforms

I have been trying to solve a 2D Poisson Equation for about 6 months now without too much prior knowledge and it has me completely stumped. I get close but seem to be missing something crucial. I’ve tried asking on this thread before but have yet to get any answers. So, I’ve decided to go the long route of finding a book or some other source on using FFTs in 2D, but have been having difficulty finding a good one. Surely someone here can point to at least one good source to help with using 2D FFTs.