Heat oven to 350°F. Arrange mini shells on a rimmed baking sheet.
Bake shells 5 minutes to crisp. Set aside to cool slightly.
Whisk sugar, cornstarch, and salt in a saucepan. Whisk in lemon juice until smooth.
Whisk in beaten eggs. Cook over medium heat, stirring, until thick and bubbling, 3–5 minutes.
Remove from heat. Stir in butter until glossy, then fold in lemon zest.
Spoon or pipe warm curd into shells, about 2 teaspoons each.
Beat egg whites and cream of tartar to soft peaks. Slowly add sugar; beat to stiff, shiny peaks. Mix in vanilla.
Top each bite with meringue, swirling or piping a small peak.
Broil 1–2 minutes, watching closely, until tips are lightly browned. Cool before serving.