Preheat oven to 350 F. To prepare filling, in top of a double boiler, whisk together egg yolks, eggs, sugar, lemon juice, and cornstarch. Place over simmering water. Cook over medium heat, stirring constantly, until thick enough to coat the back of a spoon. Do not let mixture boil Remove mixture from over water. Stir in butter. Pour into crust. To prepare meringue, beat egg whites at medium speed until foamy. Beat in cornstarch and cream of tartar until soft peaks form. Gradually beat in sugar and vanilla at high speed until stiff, but not dry, peaks form. Spoon meringue into a large pastry bag fitted with a star tip. Pipe meringue decoratively over filling to edge of crust. Bake pie until meringue is golden, 12 to 15 minutes.