You're making pastry cream for a banana cream pie for dessert tomorrow. Chilling it overnight should render it appetizingly cold by tomorrow. Dinner concludes and it's time for the pièce de résistance. To a herald of "oohs" and "ahs" you present your luscious banana cream pie. But when you cut into it, you discover a runny mess. Beneath the decadently deceptive whipped cream topping is a puddle of ooze. What went wrong?
Most likely you never brought your pastry cream to a full boil. Pastry cream is a custard, (an egg and milk mixture), thickened with flour or cornstarch. The starch, which imparts the cream with structure, contains a carbohydrate compound called amylose. Raw eggs contain an enzyme called alpha amylase that devours amylose. Boiling destroys the enzyme. Much like the famed Calvary general, your troops, (the amylose), were overrun by the Indians, (the alpha amylase), because you didn't wait for reinforcements, (extra heat). With the amylose defeated, nothing was left standing.
A custard is a mixture of eggs and milk and/or cream that can be hot or cold, sweet or savory. Most custards are desserts such as crème brulee, flan, and cheesecake. Quiche however, is a savory custard.
Custards can be stirred on the stovetop or baked in the oven. Classic stirred custards include crème anglaise and pastry cream, a.k.a. crème pâtissière. Crème anglaise does not contain starch and thus is more fluid. It is used as a sauce over cakes or fruit. Pastry cream, as stated, contains starch and therefore more body. It is used to fill tarts, Napoleons, cream puffs, éclairs and cream pies.
Despite my introductory example of a failed pastry cream, crème anglaise is actually the trickier of the two. The starch in pastry cream not only thickens it, it prevents curdling by interfering with the coagulation of the proteins. Crème anglaise, devoid of such protection can curdle very easily. Thus, while pastry cream must be brought to a full boil, crème anglaise must be gently cooked until it reaches a temperature of 170-175 degrees. It curdles at 180 so the window of success is quite narrow. Some chefs employ a double boiler, (a metal bowl resting on top of a saucepan of simmering water), which produces a more gentle heat than direct cooking in a saucepan.
Baked custards include crème brulee, flan, cheesecake, and quiche. With the exception of quiche, baked custards are usually cooked in a water bath. Once again, gentle heating is required to prevent curdling. The water bath insulates the custard from excessive heat. Baked custards are usually poured into ramekins resting inside a roasting pan filled with enough water to come halfway up the sides of the ramekins. They are done when they evince no more than a slight wiggle when the pan is shaken. It is better to slightly undercook them since carry over cooking will take place. If overdone they crack or curdle.
1 vanilla bean or 1 tablespoon vanilla extract
Half cup sugar
2 cups milk, cream, or combination thereof
4 egg yolks
Split the vanilla bean, scrape out the seeds and place them in a saucepan. Add half of the sugar and all of the milk. Heat, while whisking, until the mixture becomes hot but not boiling. Remove from the heat. Whisk the eggs in a bowl, gradually adding in the other half of the sugar until they form a ribbon. Slowly whisk half of the hot milk mixture into the eggs. Then pour the egg mixture into the saucepan with the rest of the milk. Over low heat, constantly whisk until it reaches 170-175 degrees or coats the back of a spoon, about five to eight minutes. Do not boil it. Strain the sauce. Chill it in the fridge with a piece of plastic wrap right on the mixture to prevent a film from forming.
3 tablespoons cornstarch
One pint milk
Half cup sugar
Two whole eggs and three egg yolks
Two oz. unsalted butter
Two teaspoons vanilla extract
Whisk the cornstarch in a little bit of the milk. Combine the rest of the milk with the sugar in a saucepan, bring to a boil and remove from the heat. Whisk the eggs and egg yolks with the cornstarch. Slowly pour about a third of the hot milk into the egg/cornstarch mixture, whisking constantly. Then pour the egg mixture into the saucepan with the rest of the milk. Constantly whisking, cook until it comes to a boil and thickens. Remove from heat and whisk in butter and vanilla extract. Pour into a large stainless steel bowl, cover with plastic wrap touching the cream, and refrigerate until chilled.
9 egg yolks
3/4 cup white sugar plus extra as needed for topping off each custard
1 quart heavy cream
1 vanilla bean
Preheat the oven to 325 degrees. Whisk the egg yolks with the sugar. Pour the cream into a saucepan over low heat. Split a vanilla bean, scrape out the seeds and add them to the saucepan. Bring the cream to a simmer. Remove from the heat and slowly whisk the hot vanilla cream into yolk and sugar mixture. Divide the custard into six 6-ounce ramekins, about 3/4 full. Place the ramekins in a roasting pan and fill it with enough water to come halfway up the sides of the ramekins. Bake until barely set around the edges, about 40 minutes. Remove from the oven and refrigerate until chilled. Sprinkle sugar on top of each chilled custard. Caramelize the sugar with a torch or under the broiler.