Lemon Meringue Pie Bars

In a medium saucepan, whisk together the egg yolks, granulated sugar, lemon juice, and lemon zest. Place over low heat and cook for 10 to 15 minutes, whisking frequently, until the mixture thickens and coats the back of a spoon.
Remove the saucepan from the heat. Add the cold, cubed unsalted butter, one piece at a time, whisking in between each addition until melted and smooth.
Transfer the lemon curd to a heatproof storage container. Cool to room temperature and then chill in the refrigerator for at least 3 hours.

Preheat the oven to 350℉ (176℃). Prepare a 9x9 baking pan with nonstick cooking spray and parchment paper.
In a large mixing bowl or the bowl of a stand mixer fitted with a paddle attachment, whisk together the all-purpose flour, granulated sugar, and salt. Add in the cubed, room temperature unsalted butter. Mix on low speed for about 5 minutes until the mixture turns into fine crumbs.
Pour the shortbread crumbs into the prepared baking pan. Use a flat-bottomed measuring cup or drinking glass to press the crumbs into the bottom of the pan in an even layer. Bake the crust for 15 minutes until slightly golden-brown around the edges. Remove the pan from the oven and cool the crust to room temperature.

Whisk together egg whites, granulated sugar, and cream of tartar in a heat-safe bowl. (You can use the metal bowl of your stand mixer). Place the bowl over a saucepan of simmering water on the stovetop. The water should not touch the bowl. Cook the mixture, whisking constantly, for about 5 to 7 minutes until the sugar is dissolved. Test this out by rubbing a small amount of the egg white mixture between two fingers. If it is smooth and not grainy, it is ready.
Transfer the bowl or mixture to a stand mixer fitted with a whisk attachment. You can also use an electric hand mixer. Whip the egg whites on low speed for 2 minutes until frothy. Increase the speed to medium and whip until the meringue thickens. Add the vanilla extract. Continue to whip until the meringue forms medium-stiff peaks. The time this will take may vary, but typically it is about 5 minutes or so. The meringue will appear glossy and maintain shape.

Spoon the chilled lemon curd onto the cooled shortbread crust and spread evenly using an offset spatula. Spread the meringue over the lemon curd, creating swirls and texture. Use a kitchen torch to carefully toast the meringue. If you do not have a kitchen torch, you can carefully toast the meringue underneath a broiler. Chill the bars for at least 2 hours before cutting into squares.

Store the lemon meringue pie bars in an airtight container in the refrigerator for about 3 days. Serve chilled.

Metric conversions are calculated automatically. I cannot guarantee the accuracy of this information.