Lemon Meringue Pie

Why This Lemon Meringue Pie Works

As the sugar, cornstarch, salt, and water cook on the stove, the cornstarch swells and thickens the liquid. After a minute of boiling, it goes from cloudy and loose to shiny and gel-like. When the warm egg yolks are stirred back into that hot mixture and cooked a bit more, the yolks set and give the lemon filling a smooth, firm texture that slices cleanly instead of running all over the plate. Lemon juice and zest go in at the end so the filling stays bright and doesn’t go dull from too much heat.

While the filling is still hot, the meringue goes on top. Spreading the egg whites over hot lemon filling lets a little steam rise into the meringue, which helps it puff and stick instead of shrinking. In the oven, the sugar-stabilized egg whites dry out and set into a fluffy but stable layer, and the top browns. During the long chill, the starch and eggs in the lemon layer finish firming up, so the pie holds together when sliced.

Mistakes To Avoid

Letting the lemon filling boil hard or too long after the yolks go in can scramble the eggs. Little bits of cooked egg end up in the filling, so it looks grainy instead of smooth and can set in a rubbery layer instead of a soft, sliceable custard.

Pouring the lemon filling into a cool crust or letting the filling cool before adding the meringue keeps the layers from bonding. The hot filling is what helps “cook” the bottom of the meringue; when it goes on cold filling, the meringue can slide around and weep liquid between the layers.

Beating the meringue only to soft peaks or adding the sugar too fast leaves it loose and foamy. In the oven this kind of meringue puffs unevenly, shrinks back from the crust, and often leaks syrupy beads on top instead of holding a smooth, firm shape.

Cutting and serving the pie before it is fully chilled keeps the filling from finishing its set. The knife drags through a still-warm, semi-liquid center, so slices collapse and the filling oozes out of the crust.