I want to learn how to make a CPU from scratch
I don't know about online classes, but I can tell you what I did when I designed my first CPU. So there are three steps:


Get a good Digital Design / Computer Architecture book. I strongly recommend the "Digital Design and Computer Architecture" from Harris and Harris, and also "Computer Organisation and Design" from Patterson and Hennessy (2nd edition). Of course there are tons of other books, but these are generally accepted as very good ones.
Learn an HDL (Hardware Description Language). I prefer VHDL, but you can also try Verilog
Design your processor on paper. Begin with a relatively small instruction set, and then you can add functionality or upgrade it (pipeline stages, FPU, etc.)


After you design your ISA and your architecture, you can start implementing it on the HDL you like. Then you can "download" it on an FPGA evaluation board and see your CPU running.