VanillaPlus/temp/vertrecipes/vertical_dark_prismarine_slab.json

{
    "type": "minecraft:crafting_shapeless",
    "ingredients": [
        {
            "item": "minecraft:dark_prismarine_slab"
        }
    ],
    "result": {
        "item": "vplus:vertical_dark_prismarine_slab"
    }
}