Set a 4-quart saucepan over medium-high heat. Add the olive oil and once hot, saute the onions, parsnips and celery until softened, about 4 to 5 minutes. Add the shallots and garlic to the pan and saute until fragrant, 45 to 60 seconds. Place the celery root, stock, salt and cayenne pepper in the saucepan and ring to a boil, reduce to a simmer and cook until the celery root is tender, about 35 to 40 minutes.
When the celery root is tender, remove the saucepan from the heat and puree the soup using an immersion blender (or in batches using a bar blender), until smooth. Taste, and re-season the soup if necessary and garnish with the parsley. Serve with 3 tablespoons of the sauteed lobster per soup bowl.
Set a large 2 to 3-gallon stockpot to boil over high heat. Once the water comes to a boil, immerse the lobster in the pot. Cook the lobsters for 3 minutes, remove, and chill immediately in ice water. Once the lobster is cool enough to handle, remove from the water and place on a kitchen towel draped over a cutting board. Use a mallet to crack the shells, and remove the meat from the tail, claws and knuckles. Dice the lobster meat into 1/2-inch pieces and set aside.
Set a 10-inch saute pan over medium heat and add the butter. Once the butter begins to foam, add the shallots and garlic. Saute the shallots and garlic until fragrant, about 1 minute. Add the lobster meat and season with the Essence and salt. Saute the lobster until cooked through, about 5 minutes. Add the lemon juice and raise the heat to high. Cook for 2 minutes. Add the celery leaves to the lobster and toss to blend. Remove from the heat and set aside for the soup.