craftingTable.addShaped(
    "custom_steel_boiler", 
    <item:immersive_aircraft:steel_boiler>,
    [
        [<item:minecraft:iron_ingot>,  <item:minecraft:iron_ingot>, <item:minecraft:iron_ingot>],
        [ <item:minecraft:iron_ingot>, <item:immersive_aircraft:boiler>,  <item:minecraft:iron_ingot>],
        [<item:alloyed:steel_ingot>, <item:minecraft:blast_furnace>, <item:alloyed:steel_ingot>]
    ]
);
