Fill a stockpot half way and add the lemon, celery, crab boil, kosher salt and black pepper
Bring to a rolling boil and then add the shrimp
Stir well and then remove from heat
Allow shrimp to stew in the hot liquid for 10 min.
Remove shrimp and plunge in ice bath to stop cooking
Drain the shrimp well
In a glass bowl, layer the shrimp, onion slices, and bay leaves
Emulsify the oil, vinegar and salt, either with an electric hand whisk, or in the blender
Stir the remaining ingredients
Pour over layered shrimp.
Cover and refrigerate for 24-48 hours, stirring every 6-8 hours