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

{
  "type": "minecraft:crafting_shaped",
  "group": "bark",
  "pattern": [
    "##",
    "##"
  ],
  "key": {
    "#": {
      "item": "minecraft:birch_log"
    }
  },
  "result": {
    "item": "minecraft:birch_wood",
    "count": 3
  }
}