Gaining

Add a flavored syrup of the sort made by Torani for flavoring coffee and making Italian sodas.

I blend pint of heavy cream with a pint of chocolate ice cream. It’s delicious!

You have actually used this on a feedee? I’d like to see before and afters,

Heavy cream is effective because of its fat content. But there are other foods with even more fat - there's nothing magical about heavy cream.

For example, peanut butter has TWICE the amount of calories as heavy cream per tablespoon. Making a peanut butter shake or simply eating peanut butter would get you fatter faster and be easier to digest if you're struggling with dairy.