How to access cookies from ApplicationController (Rails)

It's a hash, not a method:

cookies[:some_key]

... instead of:

cookies(:some_key)

This might work for you:

class ApplicationController
  before_filter :handle_cookies
  def handle_cookies
    # Do whatever it is you want to do with your cookies
  end
end

The before_filter method will call whatever subroutine you indicate (:handle_cookies) after cookies has been compiled into a hash. Adding this code to your application controller will mean that all the other controllers inherit it and will perform the same function.