Link to smeltingrecipe
Importing the class
Link to importing-the-class
It might be required for you to import the package if you encounter any issues (like casting an Array), so better be safe than sorry and add the import at the very top of the file.
Link to extending-abstractcookingrecipe
SmeltingRecipe extends AbstractCookingRecipe. That means all methods available in AbstractCookingRecipe are also available in SmeltingRecipe