Have you ever crafted a grindstone and an armor stand at the same time and wondered, hey, why couldn't I just use the stone slab for the grindstone and smelt it to get smooth stone slab for the armor stand, instead of smelting a new set of stone all the way through to smooth stone?
I know "decrafting" is often argued about but this is forward crafting. Start slab, end slab. Another example is sandstone slab crafts to smooth sandstone slab.
Tools to do this could be grindstone, stonecutter, maybe smithing table.