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

{
  "type": "minecraft:smelting",
  "category": "blocks",
  "cookingtime": 200,
  "experience": 0.1,
  "ingredient": {
    "item": "minecraft:stone"
  },
  "result": {
    "id": "minecraft:smooth_stone"
  }
}