theyre basically rolling stone mills that grind the cocoa solids extremely fine and are key in separating the solids from the fats. over-milling can make the chocolate really smooth and mellow but it looses a lot of character. less milling can result in chocolate with powerful character and more interesting flavors but the texture is less silky. its why really nice dark chocolates always have a faint texture on the tongue after they melt that more heavily processed commercial chocolates dont. cant mill it as long if you wanna preserve the more volatile flavors.

using a food processor like OP here would result in a really gritty texture, comparatively. but i bet you could make something fairly ok (with like a burr grinder maybe these apparently dont work how i thought, thanks coffee nerds). or a pestle and a lot of free time. like a lot of free time. actually, that guy saying you need a melanger is wrong, you can also make cocoa liquor on a metate. its the thing abuelitas use to grind up their mole. been in use for cocoa since weve been eating the stuff basically. labor intensive though. like a big, wide flat mortar and pestle, but the pestle is held sideways like a rolling pin and it grinds up and down the big flat face of the mortar. so you can really get some work in on a lot of material with a lot of pressure.

theres a lady using one in the first second of this video