Bake pie crust according to recipe (if homemade) or directions on package (if purchased). Let cool completely. Set oven to 350 degrees.
Bring water to a boil in a medium pot.
Mix 1 1/2 cups granulated sugar, salt, flour, cornstarch, lemon zest and lemon juice in a bowl. Remove water from heat, then stir sugar mixture into the water.
Beat egg yolks in another bowl, then slowly stir them into the pot along with the butter. Place over low heat. Cook, stirring, until mixture thickens enough to coat the back of a wooden spoon, about 20 minutes. Remove from heat and let cool to room temperature.
Beat cream cheese and powdered sugar, then spread over the bottom of the pie crust. Top with cooled lemon filling.
In a mixing bowl, beat egg whites until soft peaks form. Gradually beat in remaining 1/2 cup granulated sugar and vanilla. Beat until stiff peaks form. Use a spatula to spread the topping over the pie, covering the filling completely and touching the crust. With the back of a spoon, create decorative swirls.
Bake until the peaks of the swirls begin to brown, about 5 to 10 minutes. Let pie cool, then chill until cold.