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

{
  "type": "minecraft:crafting_shaped",
  "category": "redstone",
  "key": {
    "#": "minecraft:slime_ball"
  },
  "pattern": [
    "###",
    "###",
    "###"
  ],
  "result": {
    "count": 1,
    "id": "minecraft:slime_block"
  }
}