If you find the filling too runny, there are a couple of factors to consider. First, things will naturally be more fluid while it's still warm. As it cools, it will thicken up. u003cbr/u003eu003cbr/u003eSecondly, the moisture content in the apples and the cooking time will impact the consistency of the filling. If it remains too runny after cooling, mix 1 tablespoon of cornstarch with a tablespoon of water. Stir the cornstarch mixture into the apples and cook in the slow cooker for 1 more hour.