Preheat oven to 425

Prepare a deep souffle dish with 1 teaspoon butter, making sure to reach all sides to the top rim

In a large bowl, cream together 4 egg yolks (reserve whites for meringue) with Splenda adding Splenda ¼ cup at a time, until smooth and pale yellow

Add room temperature cream cheese, sour cream, vanilla, blend until very smooth

In a clean bowl, beat egg whites until stiff peaks form

Fold egg whites into cream mixture

Pour mixture into prepared baking dish

Bake at 425 degrees for 10 minutes, reduce heat to 250 degrees and bake additional 40-60 minutes

remove, and cool at room temperature for 30 minutes, refrigerate overnight