Vanilla flavor. I've got some apples I intend to bake, and some strawberries I've cut up, it'll go great with both.
While the original publisher of the recipe called it "Poor man's ice cream" and it is indeed quite inexpensive to make, I prefer to think of it as homemade soft serve. It comes out with a much softer smoother texture than traditionally churned ice cream; you're in no danger of bending a tablespoon in this stuff. It also requires no churn; it can be made with more multifunctional tools like a hand or stand mixer.