Potion brewing with squirrels is only unlocked after completing the quest Aiding the Squirrels. Raven's Cove introduces a whole new line of ingredients. 3 Oak Leaf=1 oak twig 3 Oak Twig=1 Oak Branch 3 Oak Branch=1 Oak Extract 3 Oak extract=1 Acorn Essence 3 Acorn Essence=1 Acorn Soul