The idea behind these butters is to bring out the best in whatever you are putting it on. If you have an oily fish like salmon, you want a tart butter so it isn't too rich. To make the butter tart you can use any citrus, wine or vinegar. A good combination for salmon is dill, shallots, wine or lemon. A good combination for steak is tarragon, red wine, shallots and black pepper. Swordfish might like garlic, basil and chipotle.