I think we, where English originated, are now tending to use "cookie" for the homemade variety of what we call biscuit, and "biscuit" for the drier shopbought thing, on the lines of graham crackers or Oreos, which is a very useful distinction. A Tim Tam would be like two rectangular Oreo type things, only not as dark, with a chocolate filling, and a chocolate covering. Would that port trick work with Cointreau, do you think?

I think I will now check the biscuit file on my computer, to see if it has any crumbs left in it.