The Essence Powder mod provides a way to infinitely duplicate items in Minecraft. Essentially you can turn eligible items into a powder and then eventually build up to turning it into a full block. You’ll need a mortar and pestle to first make the powder.

Do this four times and create a powder block.

Then just smelt the powder block and voila!

You can do this for a variety of items, most notably ores. But it also works for things like glowstone, ender pearls, and various food items!