Other tips I know of:

Get a bag of Ajinomoto MSG from the asian supermarket. Use it similarly to salt (e.g don't overuse it or you'll feel thirsty), but it makes anything savoury better.

A lot of times when something tastes "missing" from a dish, adding acidity can help balance the flavour. A splash of lemon juice/vinegar/worcestershire sauce etc. can really help.

and like you said, lots of delicious butter!