Bought this black walnut cookie off of Facebook marketplace for a good price. The only catch is it is warped, cracked, cupped, and twisted. It's about 4 in thick and that's plenty of material to make a coffee table, but I need some advice and guidance on making a router planing jig please.
YouTube is definitely your friend here. So many great woodworking channels. There's a woman who does this kind of project all the time, and unfortunately her channel name escapes me. If I can find it again, I'll add a comment for you.
I second this. Try searching youtube for "slab flattening jig".