When I flavor vanilla bettercream with pudding, it has been coming out gritty. Any ideas why? I use 3.4 ounces pudding to one carton of bettercream. It tastes fine, it's just gritty.

mix the pudding with a little milk first then mix with the bettercream makes a nice mousse type filling, and will be smooth. Why you have the grit is that the sugar in the pudding isn't dissolving in the bettercream

I mix my dry pudding with about 6 TBSP of HOT water to form a paste. I then blend in a little underwhipped BetterCream, smooth it out a bit, and then add that back into the rest of the underwhipped BetterCream and mix on medium for another minute, or so. No grit.

By not using any dairy product in it, you keep it shelf stable for 5 days without refrigeration.

HTH
Rae