I made my own butter milk out of lime juice and whole milk. We do not carry this item over here. I used lime zest for this cake and blueberries from Ólafsvík that we picked during our summer holidays. I love this cake it is so moist and delicious.
I made this cake last year to make use of my freshly picked blue berries. I just did not come up with anything to make. I like better to have an assignment.