I have read that blue cheese and pasta have very similar flavour profiles, so I bet this is a great combo. (foodiecrush.com)
If you can't get hold of any, substitute it with fresh lemon zest and fresh thyme for a very similar flavour profile. (KetoDietApp.com)
If you want to make the buttercream extra tasty then try adding a tablespoon of freeze - dried blueberry, strawberry, or raspberry powder and a few drops of similar flavoured Medicine Flower Extracts. (greensofthestoneage.com)