minecraft-assets/data/minecraft/recipes/polished_blackstone.json

{
  "type": "minecraft:crafting_shaped",
  "pattern": [
    "SS",
    "SS"
  ],
  "key": {
    "S": {
      "item": "minecraft:blackstone"
    }
  },
  "result": {
    "item": "minecraft:polished_blackstone",
    "count": 4
  }
}