Cut and crack the lobster and remove the meat. Slice the meat, leaving the claws whole, if desired. Place in the fridge. Break up the leftover lobster shells. Heat 1 Tbsp. of the oil in a pot over medium heat. Add the lobster shells and cook 4 to5 minutes, until rich in colour and slightly toasted. Add the stock and bring to a simmer. Simmer 15 minutes and then strain. Reserve 1 cup of the lobster stock, cool and freeze the rest for another use.
Heat the remaining oil in another pot over medium heat. Add the onion, mushrooms and garlic and cook 3 to 4 minutes. Mix in the flour and tomato paste and cook 1 minute more. Stir in the wine. Slowly pour in the lobster stock, stirring constantly. Add the paprika, cayenne and tarragon. Bring to a gentle simmer and cook 5 minutes. Mix in the peas, whipping cream, lobster meat, salt and white pepper. Simmer just until the peas and lobster are heated through. Place the vol au vent on plates; spoon the lobster mixture in and around the shells. Garnish with an herb sprig, if desired.
Note: Tenderflake vol au vent shells are available in the frozen foods aisle.