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

{
  "type": "minecraft:crafting_shaped",
  "category": "misc",
  "key": {
    "#": {
      "item": "minecraft:smooth_stone"
    },
    "I": {
      "item": "minecraft:iron_ingot"
    },
    "X": {
      "item": "minecraft:furnace"
    }
  },
  "pattern": [
    "III",
    "IXI",
    "###"
  ],
  "result": {
    "item": "minecraft:blast_furnace"
  }
}