CUSTARD PIE

MILK, CREAM, SUGAR, AND VANILLA BAKED into a pie shell can produce an extraordinarily delicate, tender custard, which contrasts perfectly with a crisp crust. Unfortunately, most custard pies are flawed. Many have a tough, overbaked ring of custard (the perimeter overcooks by the time the center is set), a soggy, milk-soaked pie crust, and/or an overly eggy taste. Although custard pie is very simple to assemble, this pie is far from foolproof.

After some initial testing, we quickly concluded that custard pie requires a fully prebaked pie crust and then a short oven time to cook the custard. When we tried partially baking the crust and then cooking the custard for some time in the oven, we inevitably turned out a pie with a soggy crust. When we used a fully baked crust and kept the oven time to a minimum (less than 15 minutes) the results were far better.

A short baking time has an added bonus: because there's not enough time for a heat differential to develop between the perimeter and the interior of the filling, the filling cooks much more evenly. Once the custard wobbles a bit when lightly shaken but feels set (not loose), the pie is done.

Of course, a short oven time for the filled pie means that the custard has to set up extremely fast. This means the custard must be thickened on top of the stove and then poured into the prebaked pie shell and baked until it achieves the texture of soft pudding. In our first round of testing, we discovered that fillings made with cornstarch as well as eggs set up much faster than those made with eggs alone. This is really not much of a surprise; the science here is pretty simple.

Cornstarch absorbs liquid when it is first added to a custard; you can see that the mixture looks thicker. Cornstarch also absorbs water as the custard bakes in the oven and water is forced out of suspension as the egg proteins bond tightly together. Since the cornstarch soaks up the liquid that arises as a custard bakes, it also helps prevent the crust from becoming soggy.

Perhaps the trickiest part of this recipe is cooking the custard on the stovetop. If cooked too little, the custard will be runny and won't set up quickly enough in the oven. If cooked too long, the custard will curdle (the eggs will bond together into bits that resemble scrambled eggs) on the stovetop. We wondered how to tell when a custard is really ready for the pie shell. Many recipes say the custard should be cooked until it coats the back of a spoon—a direction we find confusing.

An instant-read thermometer takes all the guesswork out of custard making. We found that custard cooked to 170 degrees on top of the stove won't curdle and will set up perfectly in the oven. If you don't own an instant-read thermometer, try scraping a wooden spoon along the bottom of the saucepan as the custard cooks. When the custard is thick enough to adhere to the edge of the spoon and form a ridge on the spoon, it is done.

The final issue was the type of dairy to use in the custard. We found that skim milk gave the custard a hollow taste and a thin texture. Whole milk provided good flavor but did not set well. Half-and-half was better-tasting but still did not set up properly. Light cream set up fine but tasted a bit fatty. Heavy cream was too much of a good thing. After some tinkering, we settled on a ratio of two cups whole milk to one cup heavy cream—a mixture with more fat than straight half-and-half but less fat than light cream.