Heat olive oil in a large pot over medium heat. Add butter and melt. Add the shrimp shells, shallots, celery, carrots, parsley, thyme, bay leaves, lemon zest, tomato paste and cayenne. Cook, stirring every occasionally, until the shells are red and the vegetables are tender, about 10 to 12 minutes.
Remove from heat and add sherry. Ignite the sherry with a wand lighter and cook until the flame subsides. Return the pot to the heat, sprinkle in flour and stir. Cook for another 2 minutes. Add seafood stock to deglaze. Stir browned pieces from the bottom of the pot. Add cream, milk, and HIDDEN VALLEY RANCH and bring to a boil. Turn the heat to low and simmer until reduced and thickened, 40 to 45 minutes. Strain into a clean pot and season with salt and pepper. Bring bisque to a simmer.
Chop shrimp into small pieces and add to bisque. Cook about 3 minutes until shrimp are done. Taste for seasoning and garnish with HIDDEN VALLEY RANCH DRESSING and chives.