How to properly make maple foam?
It's not exactly what people mean by culinary foam, but you can make maple whipped cream. (It seems kinda like the original recipe you found was trying to do this, except it forgot that you can't really make whipped milk.) There are a lot of recipes you can find for this online. They probably won't be as concentrated maple flavor as a more pure maple foam, so a couple thoughts:


You can always reduce the maple syrup, so that you can add more maple flavor without adding so much water that you destabilize the cream.
You could use manufacturing cream, which has even more fat than heavy cream, so it's more stable when whipped, and you'll be able to add more maple.