Set a fine-mesh strainer over a glass bowl. Set aside.
In a medium saucepan, combine eggs, sugar and lemon zest; whisk until smooth.
Add lemon juice and butter and cook over medium heat, whisking constantly, until mixture has thickened, 7 to 9 minutes. Watch carefully after foam on top dissipates. Do not allow mixture to boil.
When mixture is thick, immediately pour through a strainer into bowl. Cover surface with plastic wrap, pressing directly onto surface of curd, and refrigerate for at least 3 hours and up to 3 days.
For the Meringue
Preheat oven to 250 deg F and line a large, rimmed baking sheet with a silicon mat.
Combine egg whites and vanilla in a clean, dry mixing bowl. Beat with a clean, dry whisk attachment on medium speed until foamy, about 30 seconds. Increase mixer speed to medium-high and whip until mixture is white and has increased in volume, about 1 minute.
With mixer running, add 1 cup sugar, one tablespoon at a time and cream of tarter. Continue to whip until whites are shiny and form stiff peaks, 3 to 4 minutes longer. Mixture should be thick, stiff and glossy.
Scoop meringue mixture into 6 mounds (about ¾ cup each), spaced several inches apart. Use the back of a spoon to gently spread meringue into 4-inch rounds or egg shapes and to create an indentation in center of each.
Bake meringues until firm and dry but not brown, about 1 hour 30 minutes. Do not open oven door while baking. Turn off oven, open oven door slightly, and let meringues sit in cooling oven until completely dry, about 2 hours.
Divide lemon curd among meringues (creating “yolks” in centers) and serve immediately.