Step 1

Heat the oven to 350°F (175°C).

Step 2

In a large bowl, whisk together the sweetened condensed milk and egg yolks. Add the lime juice and whisk until smooth. Whisk in the lime zest.

Step 3

Pour the filling into the par-baked crust, making sure to scrape the entire contents from the sides of the bowl into the pie. Bake until the outer edges of the pie have solidified, but the center of the pie looks slightly fluid under the surface when the pie is jiggled, 15 to 20 minutes.

Step 4

Meanwhile, make the meringue (see below).

Step 5

When the filling is done, pile the meringue on top of the pie, making sure the meringue touches the inner edge of the crust, not just the curd, to prevent sliding. Use the back of a hot, wet spoon to create a wavy texture with peaks and valleys, or transfer the meringue to a pastry bag fitted with a fluted tip and pipe it on, starting at the outer edge and working your way to the center.

Step 6

Set the oven rack so that when the pie is on it, the very top of the pie is 3 to 5 inches (7½ to 12 centimeters) from the heating element. Set the pie on a baking sheet so you can move it in the oven more easily.

Step 7

Turn the broiler on high. When the heat is in full effect, place the pie under the broiler and set a timer for 1 minute. Broiler heat varies wildly from oven to oven, so keep a close eye on the pie for the entire time it is under the broiler, carefully rotating the baking sheet if needed to toast the meringue evenly. Heat until the peaks of the meringue turn golden brown, anywhere from 1 to 3 minutes, depending on your oven.

Step 8

Transfer the pie to the fridge until cooled completely, about 4 hours. To serve, slice with a hot, wet knife in order to avoid dragging the meringue. The pie will keep for up to 5 days, covered, in the fridge.

Step 9

Make sure the egg whites are completely free of any yolk and that your bowl and mixer attachments are completely clean and non-greasy. Otherwise, the egg whites will not whip properly.

Step 10

In the bowl of a stand mixer with the whisk attachment or in a large bowl with a hand-held mixer, beat the egg whites and cream of tartar on high until they are white and foamy and hold soft peaks.

Step 11

Meanwhile, in a saucepan, stir ¼ cup (60 milliliters) water and the sugar over high heat until the sugar has dissolved and the syrup reaches a strong boil. The temperature on a candy thermometer should read 240°F (116°C) (this is the soft ball stage—if you carefully drip a little syrup into a glass of cold water, it will form a soft, malleable ball). Remove from the heat.

Step 12

With the mixer running, pour the hot sugar syrup in a thin stream into the foamy egg whites. Continue beating until the meringue holds the pattern of the whisk or beater as it spins. The texture should be voluminous but still silky. If it is looking fluid and sticky, feel free to keep beating until it firms up. (Even if you overwhip it, it can be saved—see Author Notes.)

Step 13

Add the vanilla and salt and beat just until combined.

Step 14

Use the meringue immediately to assemble a meringue pie according to the instructions in the recipe, or use as a pie sundae topping.