Twine/src/main/resources/data/twine/recipes/large_backpack.json

{
    "type": "minecraft:smithing",
    "base": {
        "item": "twine:small_backpack"
    },
    "addition": {
        "item": "minecraft:gold_ingot"
    },
    "result": {
        "item": "twine:large_backpack"
    }
}