some of the best dietary advice I've ever seen.
I can buy a chorizo from my local supermarket that clocks in at about 60g of protein and 1000 calories, pretty much all from fat.
Cook that up with some onions, garlic, peppers, tomatoes, spinach, etc., make a basic carbonara sauce with an egg, some yoghurt and lemon juice, add as much pasta as you like and you've got a god damn sexy high calorie feast full of nutrients that takes like 15 minutes to prepare.
Just an example of how knowing your way around a kitchen makes the whole gaining weight thing easy and delicious.
Sure, sometimes you'll have to do gross things like eat an entire packet of ground beef mixed into a half dozen eggs because you missed a meal and need to make up the deficit, but learning to cook is still your greatest ally when it comes to gaining weight, IMO.