There are tons of recipes on the internet but they are all just variations on the same thing. Butter, coconut oil, and heavy cream beaten or emulsified in coffee. The amount of these fats that you use determines how high calorie it is but there is a point I am sure where it just becomes undrinkable. There are also lots of recipes out there for fat bombs which may be of help to your friend as well. If the friend is non diabetic and looking for more calories, make the fat bombs with sugar or honey instead of sweeteners.