Instructions: Preheat oven to 350F 175C. In a saucepan, combine rhubarb, strawberries, sugar, and cornstarch. Cook over medium heat until fruit is tender and mixture thickens, stirring occasionally. Stir in vanilla extract. Remove from heat and let cool. Place tartlet shells on a baking sheet. Spoon the cooled rhubarb-strawberry mixture into the tartlet shells. In a mixing bowl, beat egg whites with cream of tartar until soft peaks form. Gradually add sugar and vanilla extract, continuing to beat until stiff peaks form. Spoon or pipe meringue onto the filled tartlet shells, covering the fruit mixture completely. Bake tartlets in preheated oven for 10-12 minutes, or until meringue is lightly browned. Allow tartlets to cool before serving. Enjoy!