Peel the garlic and shallot. Chop both very finely. Add the shallot and half of the garlic to a medium saucepan together with 2 bay leaves and a teaspoon of butter. Place this over medium heat and gently cook the shallot and garlic for a few minutes until soft and a little golden. Season with a little pepper and salt.
Then remove them from the pan to a clean plate and cover with some tinfoil. Don’t wipe the pan clean! The browned bits will add extra flavor to out celery sauce. Add the remaining butter, chopped onion, remaining chopped garlic, 2 remaining bay leaves and thyme sprigs.
Gently brown the onion and herbs for 2 to 3 minutes. Then add the chopped celery.