This explains why butter sweats when left on the kitchen worktop on a hot day—the water separates from the fat as it melts. At even warmer temperatures—in a pan over a hot burner, or in the microwave—butter’s fat and water will immediately separate. Melted butter, then, is a broken emulsion, hardening as it cools, never to return to its former miraculous state.
Take care of its emulsion and butter will lend creaminess to everything from jambon-beurre, the classic Parisian ham and butter baguette, to chocolate truffles. The precise temperatures prescribed for butter in recipes are not arbitrary: butter at room temperature is more pliable, allowing air to be worked into it to lighten cakes, or to combine more readily with flour, sugar, and eggs for tender cakes and cookies, or spread evenly onto a baguette, to be topped with ham. As I’ll explain later, it’s also important to keep butter cold in order to preserve its emulsion and prevent it from interacting with the proteins in flour when making doughs for flaky pastries, including All-Butter Pie Dough.
Julia Child once remarked, “With enough butter, anything is good.” Put her advice into practice by using butter to make another emulsion: butter sauce. Temperature is crucial with butter-water emulsions. The key is to start with a warm pan and cold butter. For a simple pan sauce, after removing a steak, fish fillet, or pork chop from the pan, tip out any excess fat. Place the pan back over the heat and add just enough liquid—water, stock, or wine—to coat the bottom. Using a wooden spoon, scrape any delicious crusty bits into the sauce and bring it to a boil. Then, for each serving, add 2 tablespoons of very cold butter into the pan and swirl over medium-high heat, letting the butter melt into the liquid. Don’t let the pan get so hot that the butter sizzles; as long as there is enough water in the sauce, you’ll be fine. Once you see the sauce begin to thicken, turn off the flame and let the butter finish melting over residual heat, but don’t stop swirling. Taste for salt and, if needed, add a squeeze of lemon or splash of wine. Spoon over the food and serve immediately.
The same method works for making butter-water sauces to coat noodles or vegetables. Do it directly in the pasta pan, as long as it’s hot enough and the butter is cold. Make sure there’s enough water in the pan, and swirl, toss, swirl to make the sauce and coat the pasta all at once. Add pecorino cheese and black pepper and you’ve got Pasta Cacio e Pepe, the classic Roman dish that’s even more delicious than macaroni and cheese.
Breaking and Fixing Emulsions
Some emulsions will naturally break with time, and others will break if fat and water are combined too quickly, but the most common way to ruin one is to allow its temperature to swing. Some emulsions must remain cold, and others warm. Yet others must be at room temperature. Heat a vinaigrette, and it will break. Chill a beurre blanc, and it will break. Each persnickety emulsion has its comfort zone.
Sometimes, you seek to break an emulsion, as when you melt butter to clarify it. Other times, it’s a disaster. Heat a chocolate sauce too quickly and it will break into a greasy, undesirable mess that even I wouldn’t pour over ice cream after the longest day. But, as important as it is to be careful with emulsions, ruining one isn’t the end of the world, and you almost always have some recourse.
If the magic holding together your mayonnaise expires and your emulsion breaks, don’t worry! The best way to learn how to fix a broken mayonnaise is to break it once deliberately so you can figure out how to salvage it.
Here’s the mind-bogglingly simple solution: get out a new bowl, but keep the same whisk. If you have only one bowl, scrape out the broken mayonnaise into a measuring cup with a spout or, failing that, a coffee cup, and clean the bowl.
Bring the clean bowl to the sink and spoon in half a teaspoon or so of the hottest water you can coax from your tap.
Using your oily, eggy whisk, start whisking the hot water maniacally, until it starts to foam. Then, treating the broken mayonnaise as if it were oil, add it drop by drop, continuing to whisk with the urgency of a swimmer escaping a shark. By the time you’ve added half of it back, it should start to resemble a proper mayonnaise again, perfect for slathering on a lobster roll. If this fails you, then begin the entire process over with the insurance a new egg yolk provides, and add the broken mayonnaise back in, a drop at a time.
In the future, if, while whisking together any emulsion, you notice things start to head south, keep these tips in mind. First, as soon as you suspect that you are on shaky ground, stop adding fat. If the emulsion isn’t thickening and the tines of the whisk aren’t leaving visible tracks, then for heaven’s sake stop adding oil! Sometimes, all that’s called for at this point is a good strong whisking to bring things back together.
You can also add a few chips of ice along with the first whiffs of doubt. If you don’t have ice on hand, a tiny splash of cold water from the tap will suffice to regulate temperature and keep the peace.
Flaky and Tender
Two proteins in wheat—glutenin and gliadin—comprise gluten. When you combine wheat flour and liquid to make dough or batter, these proteins link up with one another into long chains. As dough is kneaded or batter is mixed, the chains develop into strong, extensive webs or the gluten network. The expansion of these webs is called gluten development, and it’s what makes a dough chewy and elastic.
As gluten develops, dough becomes chewier. This is why bread bakers use flours with relatively high protein content, and work hard to knead doughs for long periods of time to create crusty, chewy country loaves. Salt also preserves the strength of the gluten network. (That’s why the mixer strained with effort when I belatedly added the salt to my pizza dough as a young cook at Chez Panisse.) But pastry chefs generally seek tender, flaky, and moist textures, so they do everything they can to limit or control gluten development, including using low protein flours and avoiding overkneading. Sugar and acids such as buttermilk or yoghurt also discourage gluten from developing, so adding them early on will tenderise pastries.
Too much fat can also inhibit gluten networks from forming. By coating individual gluten strands, fat prevents them from sticking to one another and lengthening. This is where the term shortening comes from, because the gluten strands remain short instead of lengthening.
Four main variables will determine the texture of any baked good (and some nonbaked ones, such as pasta): fat, water, yeast, and how much the dough or batter is kneaded or worked (see illustration on opposite page). The particular way and degree to which fat and flour are blended together, along with the type of flour and type and temperature of the fat, will also affect a pastry’s texture:
Short doughs are the epitome of tenderness, crumbling and melting in your mouth. Here, flour and fat are blended together intimately, resulting in a smooth, homogeneous dough. Many of the shortest recipes, such as shortbread cookies, call for very soft or even melted butter, in order to encourage this now fluid fat to quickly coat individual flour particles, preventing gluten webs from forming. These doughs are often soft enough to press into the pan.
Rather than crumbling, flaky doughs break apart into flakes when you take a bite. Think of classic American pies and French galettes, with crusts sturdy enough to hold up to a mile-high pile of apples or juicy summer fruits, but delicate enough to produce thin, uneven flakes when sliced. To create that strength, some of the fat is worked into the flour, and a minimal amount of gluten is developed. To achieve the signature flakes of a perfect pie or galette crust, the fat must be very cold so that some of it can remain in distinct pieces. Roll out a properly made pie dough and you’ll see the chunks of butter. When you slide the pie into a hot oven, the cold pieces of butter, entrapped air, and steam from the water released by the butter, all push apart the