Preheat oven to 350 degrees F (175 degrees C). Grease 24 mini tart pans.
In a large bowl, cream together butter and 1/2 cup sugar until light and fluffy. Beat in egg and vanilla. Gradually stir in flour and salt. Press into the bottom and up the sides of the prepared tart pans.
Bake for 15 minutes in preheated oven, until golden brown. Meanwhile, in a medium saucepan, mix together the lemon juice, 1/4 cup sugar, and cornstarch. Cook over medium heat, stirring constantly, until mixture thickens. Remove from heat.
In a medium bowl, beat egg whites until foamy. Gradually add 1/4 cup sugar, beating until stiff peaks form. Fold in the lemon mixture. Spoon into the tart shells.
Bake for an additional 15 minutes in the preheated oven. Let cool before serving.
Interesting Facts
Meringue is a type of foam made with egg whites and sugar.
Lemons are a type of citrus fruit.
Mini tart pans are used to make individual treats.