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

{
  "type": "minecraft:crafting_shaped",
  "category": "misc",
  "key": {
    "#": {
      "tag": "minecraft:planks"
    },
    "-": {
      "item": "minecraft:stone_slab"
    },
    "I": {
      "item": "minecraft:stick"
    }
  },
  "pattern": [
    "I-I",
    "# #"
  ],
  "result": {
    "item": "minecraft:grindstone"
  }
}