Easy prep for this one. Dice the onions and celery, mince the garlic and cilantro, peel and de-vein the shrimp and you are ready to go.
Melt butter in saucepan over medium heat.
Add the onions, celery and garlic along with a pinch of salt and pepper, and cook over medium heat until softened, stirring often.
When the vegetables have softened, add the flour, cooking and stirring for about 3 minutes, or until the flour-butter paste is a light golden brown. What you have just made is called a roux, or a mixture of cooked fat and flour. Normally a roux is not made with vegetables in it at the beginning, but to me, this is a great way to add flavor.
Whisk in the cold stock or clam juice. Make sure the liquid is cold. The rule for roux is to add cold liquid to a hot roux or hot liquid to a cold roux, otherwise, your sauce will be lumpy.
When well blended, add the cilantro and taste for seasoning. Add a pinch more salt and/or pepper, if necessary.
Cook for 3 minutes. If the sauce is too thick, add a little more fish stock or clam juice.
Add the shrimp. Cover and cook for 5 minutes or until sauce is thick and flavors are blended.
Add lime juice just before serving.
Serve over rice or pasta, and garnish each serving with a some fresh cilantro.