I have tried making a German recipe for buttercream. It calls for pudding and butter. Everytime I make it, the recipe does not turn out right, any suggestions? Maybe I am missing an ingredient?
Any help would be appreciated.
Thank you.

What do you mean when you say "pudding"?.
When I make GBC, I use fresh, chilled creme patisserie and have never had a problem. I usually use 12oz of butter to 1 lb creme. I beat the butter first with the paddle,add the creme in quarters, then beat for 3 minutes or so until it's light and fluffy.
Are you using an instant pudding? That could be the problem...all those instant starches break down after time.
HTH