Compound butters, be they garlic, maitre d' or harissa are all well and good, but for when you want to be really nice to both yourself and that prime Rib Eye you've just got from Well Hung and Tender:
Take a bunch of tarragon and strip the leaves. Chop finely and throw them into a small pan with 125 ml or so of sherry, red wine or champagne vinegar (or a mixture of the 2 or three, sometimes I'll also use tarragon vinegar), 2 shallots (or 1 large banana shallot) and a teaspoon of black pepper that's been bashed and cracked with a mortar and pestle.
Reduce this down 'till it's almost dry, do it slowly or it'll burn and the vinegar will stink the kitchen out.
While that's reducing place a block of unsalted butter, preferably French, weighing about 225/250g into another small pan and melt it gently.
When the reduced tarragon has cooled place mixture in a heat proof bowl and beat in an egg yolk. Now place the bowl over a pan of barely simmering water and beat in another 3 egg yolks, beat constantly until the eggs look foamy and thicker. This isn't scrambled eggs so if it looks like it's beginning to scramble or split, take it away the pan and add just a touch of cold water and whisk furiously; it may work and recombine, if not - go back to step 1. Also, use the best and freshest freerange, organic eggs you can get your mitts on, don't even waste your time with this if you're going to use some supermarket value egg that's been in hte fridge for a couple of weeks. Also also, have the yolks at room temperature before using.
When the yolks and reduction are combined, foamy and thicker, start to add the warm butter, spoonful by spoonful. Do this carefully because you don't want any milk solids (that white stuff in the bottom of the pan) getting into the sauce, keep whisking and whisking. Once the butter's almost all gone (except for the white crud), taste the sauce.
Season it with some salt and pepper, and serve it immediately beside that steak and some chips. Real chips, not frozen or oven chips, you've just made a kick-ass Bearnaise so why spoil it with frozen chips?