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

{
  "type": "minecraft:crafting_shaped",
  "pattern": [
    "##",
    "##"
  ],
  "key": {
    "#": {
      "item": "minecraft:polished_blackstone"
    }
  },
  "result": {
    "item": "minecraft:polished_blackstone_bricks",
    "count": 4
  }
}