Preheat the oven to 180°C (350°F). Prepare the keto graham cracker crust and make two batches of the keto lemon curd according to their recipes.

Pour the lemon curd into the prepared crust, filling to about two-thirds full. If there is extra curd, reserve it for another use.

Place a clean, dry mixing bowl and beaters on the mixer. Make sure there is no yolk on the egg whites.

Add the 2 large egg whites to the bowl and begin beating on medium speed until soft peaks form.

If using the optional cream of tartar, add the 1/4 teaspoon now. With the mixer running, slowly add the 1/2 cup sugar-free powdered sugar in a steady stream, then continue beating until the meringue is thick, glossy, and holds stiff peaks.

Spoon or spread the meringue immediately over the lemon curd, spreading it all the way to the crust edges to seal.

Place the pie in the preheated oven and bake 5–7 minutes, until the meringue is lightly golden on top. Remove from oven and cool before serving.