minecraft-assets/assets/minecraft/models/block/composter_contents1.json

{
    "textures": {
        "particle": "block/composter_compost",
        "inside": "block/composter_compost"
    },
    "elements": [
        {   "from": [ 2, 0, 2 ],
            "to": [ 14, 3, 14 ],
            "faces": {
                "up": { "texture": "#inside", "cullface": "up" }
            }
        }
    ]
}