How to thicken a sour cream-based pastry cream? I did some research, but can't find the answer to my problem: I need to thicken the cream that I am making for my layered cake. The cream is made of sour cream and sweetened condensed milk. The cream, the way it is - is runny. It is good (and also preferable) for getting the layers of my cake moist. But then, I need to keep a layer of the same in between the layers of the cake and that's where I face the problem: it all runs off. I would like to thicken it. What I had in mind is consistency of a vanilla pudding or, maybe, even a bit thinner. I tried xanthan gum, but I don't like the texture: it is too slimy. I tried tapioca flour, but nothing happens (maybe I did something wrong). Anyone has the experience? Until now, I kept thinking that heating was not an option and that I had to keep the sour cream cold, but now I thought that maybe it is what I will have to do. I am just not sure if heating it will degrade its quality as the end product will be the type of cake that needs to be refrigerated.
I'm wondering if mixing in some cream cheese in addition to, or in place of a portion of the sour cream, might help thicken things without altering the taste profile too much.

Sour cream is roughly 73% water, while cream cheese is only around 53% water. That may be a way to reduce some of the water content without having to resort to heat.