When I make garlic butter for fish, it does tend to be a case of "garlic with a little butter added because it's not socially acceptable to consume a whole bulb on your own".
120g Salted Butter
4-5 Garlic cloves, grated
3 Spring Onions, chopped
Lemon zest
Parsley
Mix the ingredients together with a fork, place in a clingfilm covered-bowl in the fridge overnight.
You can eat it straight away I suppose, but leaving it seems to mellow the whole concoction a little.