Table leg idea
When I make slab benches, I splay the legs 15° toward the sides and 15° toward the ends. I made a jig to hold the slab at the correct angle to locate and bore holes with forstner bits in the underside of the slab. The hole has to be inset such that the foot of the leg falls under the corner of the slab (doesn't stick out beyond the top). The longer the leg, the further inward from the side and end the hole has to be.
I join the legs to the slab with a blind foxtail mortise. I drill the holes with a forstner bit slightly smaller than the leg diameter. I shave the top of the leg with a spoke shave so it's a snug fit into the hole. Cut a slot into the end that goes into the hole, make sure the slot is not deeper than the hole depth, so the slot won't show when the leg is attached. Make a wedge slightly thicker, narrower, and shorter than the slot. Put glue in the slot, glue in the hole, put the wedge in the slot, and drive the leg into the hole with a mallet, put a piece of scrap wood on the leg to protect it from the mallet blow. Make sure the slot in the leg goes into the slab across the grain. If the slot is lined up with the slab grain, it could split the slab.
I drill the leg holes about 3/4 the depth of the plank thickness (I usually use 4" slabs). I use tree limbs of the same species as the slab for legs, but you could use this method for any shape leg.