eat like Renee and you'll gain mass
calorie rich and useful are not necessarily the same thing.
If you want to grow muscle, you need to start thinking of taking up training - otherwise why would your body want to put on any muscle? Muscle is expensive to maintain from your bodys point of view and it would much rather just pack on fat.
Start snacking on nuts in the first instance. They are calorie rich, but still full of goodies, good fats, minerals, protein etc. Examples: mixed nuts bags, almonds, cashews (expensive!), pistachios etc.
Fat is calorie rich of course, so perhaps if you have a salad, pour a bit of olive oil on it, or if you are having pasta or rice, pour some olive oil on that too - it's tasty and boosts the calorie content.
There are millions of little tricks, but thats just two of them for now - others probably have their own tricks as well?