For my money, the very best classic steak sauce you can make at home, a sauce that will wow your guests with its flavor and elegance, and—most importantly—a sauce that can be made start to finish in under half an hour, is béarnaise. If you want to get straight to the action, jump straight to the step-by-step here.
I've spent plenty of time and internet real estate talking about all of my favorite ways to cook steakhouse-quality steaks at home, starting with how to dry age your own to how to cook it on a grill or in a pan, or even how to cook it sous-vide style with a beer cooler and a blow torch. We've debunked steak myths and proven that you should flip your steaks multiple times for the best results.
But perfect steak alone does not a meal make. Actually, I take that back. A perfect steak requires no embellishment beyond salt and pepper, but just because it doesn't need it doesn't mean that a nice sauce to go with that steak isn't welcome from time to time. I have a dress shirt that I like to wear with the top buttons undone on most occasions, but I'll break out the necktie every once in a while for those special nights out. (You know, the ones when you put on socks and shoes.)
Here's the thing: It's relatively easy to get better-than-steakhouse quality steak at home. But making a restaurant-quality sauce? Much more difficult. Classic French steak sauces like espagnol or its derivatives bordelaise or Robert, for instance, require intensely rich, gelatin-packed demi-glace. Those sauces are multi-day affairs that nobody but the most ambitious home cooks will even attempt. Compound butters flavored with herbs and aromatics are a great option for a home-cooked steak, as is a simple pan sauce, but they're lacking in class and panache. That's where béarnaise comes in. It's as classy as sauces come, it requires nothing that you can't find at your average supermarket, and it's quick to make.
The catch (there's always a catch) is that made with the classic technique, it's very easy to mess up. Like hollandaise and mayonnaise, béarnaise is a fat-in-water emulsion, in this case butterfat emulsified into a reduction of white wine and vinegar flavored with shallots, tarragon, and chervil, all bound and thickened with egg yolks.
And just like with hollandaise,* the ways to mess it up are plentiful. Traditionally, you'd make béarnaise by reducing white wine and vinegar with shallots and tarragon to a flavorful syrup, then strain it into a bowl. Next, you'd whisk egg yolks into the mixture and beat them vigorously over a double boiler until the eggs begin to thicken. Then you'd slowly drizzle in clarified butter while whisking until a thick emulsion with the texture of warm mayonnaise is formed. Finally you'd season it with salt and stir in some chopped tarragon and chervil. Add the fat too fast and you break your emulsion. Heat it up too much and it turns into scrambled eggs. Don't heat it enough and you'll have a thin, wet sauce instead of a rich, meat-coating sauce. You get the picture.
In fact, béarnaise is technically a derivative of hollandaise sauce, one of the five French mother sauces.
Fortunately, we can use the exact same technique we use to make that foolproof hollandaise to make a foolproof béarnaise. The key is to completely forgo the double boiler, instead heating up the butter and using its residual heat to cook the egg yolks. By placing the yolks and the wine reduction in the bottom of a tall container that just barely fits the head of a hand blender, we can create a strong vortex that then pulls hot butter down towards the blades of the hand blender, creating a strong, stable emulsion.
Check out this video about hollandaise for a bit more of the science.
How to Make Foolproof Béarnaise, Step-by-Step
Step 1: Make Your Reduction
Combine a quarter cup of white wine vinegar, a half cup of white wine, some chopped shallots, and a few stems of tarragon and chervil (optional) in a small saucepan, then let it simmer over moderate heat until it's reduced to just about a tablespoon and a half of syrupy golden liquid. Let the liquid cool just a bit so that it doesn't cook your egg yolks when you add it.
Step 2: Strain and Combine
Next strain the liquid into a cup that just barely fits the head of an immersion blender, along with 2 egg yolks and a pinch of salt.
You wan the liquid to cover the head of the blender, like this.
Meanwhile, melt a stick and a half of butter in a saucepan over moderate heat, swirling the pan until the foaming subsides and the butter registers around 200°F on an instant-read thermometer.
Step 3: Drizzle in Butter
With the immersion blender running, slowly drizzle in the melted butter, lifting the head of the blender up and down to make sure that the butter is smoothly and evenly incorporated.
Continue adding the butter in a thin, steady stream until it's all been added. The mixture should be about as thick as pancake batter at this point. Season it to taste with salt.
I actually kind of like the texture like this, though for a truly classic béarnaise, you want it to thicken up just slightly. If you prefer it thicker, transfer the mixture to a heavy metal bowl or a saucier and place it over low heat, whisking vigorously and constantly until it reaches the desired texture.
Stir in some chopped tarragon and chervil (I sometimes also add a few tablespoons of minced chives), and you're ready to serve.
Steak never had it so good.