minecraft-assets/data/minecraft/recipe/sandstone.json

{
  "type": "minecraft:crafting_shaped",
  "category": "building",
  "key": {
    "#": "minecraft:sand"
  },
  "pattern": [
    "##",
    "##"
  ],
  "result": {
    "count": 1,
    "id": "minecraft:sandstone"
  }
}