Heavy cream and its usefulness for gaining is more complex than people realise. It has a lot to do with how its used and consumed.
For starters, drinking it straight is not particularly effective. If it doesn't bind to anything in your guts, it basically just acts like a lubricant. The equivalent of drinking oil. The secret is binding it to something else so that it can have the time to be digested.
In our experience, substituting milk with heavy cream for making a box of instant pudding is actually pretty effective! The gelatin in the pudding mix binds really well and makes it more solid. Can be a little difficult to eat the whole thing unless you've trained some stomach capacity, but one box of pudding and a pint of good quality heavy cream is nearly 2k calories on its own.
Some other suggestions for binding it to something: milkshakes, smoothie powders, blended fruits, protein powder, oatmeal, basically anything thick or solid that appreciates milk.
If you're used to dairy products, this isn't a bad way to force some extra calories, but you gotta be wary of cholesterol. Heavy cream is pretty high in cholesterol, so over-relying on heavy cream, or having an already high cholesterol diet and adding it, can lead to heart problems.
YMMV
2 days