Add butter to a large saucepan on medium heat. Saute' yellow onion
and celery until fragrant, about 3min. Add all other ingredients
besides the flour, lemon, broth and shrimp. Simmer for about 5
min. Sprinkle flour over mixture and stir until it starts to clump
together,(sprinkle a little more if needed). Stir in broth and
simmer for 3 min.