Schema.org for complex or multi-part recipes - schema.org

Question

I am trying to determine how to mark up a Recipe in Schema.org where the recipe has multiple sub-recipes.
For example: A Victoria Sponge might have:
Set #1: Ingredients, preparation steps, and prep/cook times for the Sponge
Set #2: Ingredients, preparation steps, and prep times for the Filling
Set #3: Ingredients, preparation steps, and prep times for the Icing/Topping
I have seen recipe examples where all the ingredients are together in a list and the instructions/steps then attempt to determine which is use at which point, but this is not really satisfactory.
Obvious approaches are: separate recipe components, or perhaps an "array" of ingredients and steps. And, I can see it ought to be possible using a HowTo structure of steps of sub-recipes, but cannot see how.
I'd really like to see an example that has actually been tried. I am using JSON-LD, but anything that demonstrates a principle would be much appreciated!

Answer 1

If you need to group the ingredients per "sub-recipe", you have to provide multiple Recipe items, because the recipeIngredient property is only defined for the Recipe type.
I don’t know if such a model was intended, but it seems to be possible with the specified expected values. It works if you think that a Recipe instruction step can be a Recipe itself.
JSON-LD example
<script type="application/ld+json">
{
"#context": "http://schema.org",
"#type": "Recipe",
"recipeInstructions": {
"#type": "ItemList",
"itemListElement": [
{
"#type": "ListItem",
"position": 1,
"item": {
"#type": "HowToStep"
}
},
{
"#type": "ListItem",
"position": 2,
"item": {
"#type": "HowToSection",
"steps": {
"#type": "Recipe"
}
}
},
{
"#type": "ListItem",
"position": 3,
"item": {
"#type": "HowToStep"
}
}
]
}
}
</script>
Example explanation
The main Recipe has three instruction steps.
ListItem is used to give each step a position (so that the ItemList is ordered).
The first and the last steps are HowToStep items. A HowToStep is a list that can take HowToDirection and HowToTip items as list entries.
The second step is a HowToSection item. HowToSection is a "sub-grouping of steps". Its definition gives this example, which seems to fit your case:
steps for making a pie crust within a pie recipe
Now, instead of representing this HowToSection’s steps again as a list of HowToStep items, the sub-recipe is given as Recipe item. This is possible because steps has CreativeWork as expected value, of which Recipe is a sub-type.
(Note that Google’s SDTT doesn’t recognize the HowTo types yet. They were introduced with the current Schema.org version 3.3, which was released last month.)