For lobster bisque:
Place butter and olive oil in a large saucepan over medium heat.
Sauté the onions, celery, and fennel for 6-7 minutes or until they are tender.
Add the lobster shells and tomato purée and continue to cook for 1-2 minutes.
Add the flour and stir until combined and continue to cook for another 1-2 minutes.
Add the cognac and stock and continue cooking for 30 minutes. While cooking, stir and scrape the bottom of the sauce pan with a wooden spoon to loosen any brown bits.
Add the heavy whipping cream and bring mixture to a boil and continue cooking for 15 minutes.
Add the cayenne pepper, garlic, and chervil and stir to combine.
Remove the lobster shells and carefully place mixture in a blender and blend on medium for 15-20 seconds, or until combined and smooth. Stop the blender to scrape the sides and blend for another 5 seconds.
Pour the bisque through a fine strainer lined with cheesecloth to remove any shell pieces.
Pour the bisque back into the saucepan over medium heat and bring it back to a boil.
Season to taste with salt and pepper. Set aside.
For mashed potatoes:
Place the potatoes in a large stockpot of boiling, lightly salted water over high heat for 15 – 20 minutes or until the potatoes are soft.
Drain the water and whip the potatoes with a hand held mixer on low speed until soft.
Add butter and heavy whipping cream and mix until combined.
Season to taste with salt and pepper. Set aside.
For lobster and scallop fisherman’s pie:
Preheat the oven to 350 degrees.
Place butter and olive oil in a large stockpot over medium heat.
Sauté the onions, celery, and carrots for 6-7 minutes or until they are tender.
Add the flour and stir until combined and continue to cook for another 1-2 minutes.
Add the brandy and stir while cooking for 1-2 minutes to cook off the alcohol.
Add the scallops and lobster bisque and stir to combine. Continue to cook for another 8-10 minutes or until the mixture comes to a boil.
Add the cooked lobster, tarragon, and hot pepper sauce and stir to combine. Season to taste with salt and pepper.
Carefully pour the mixture into a 3 quart baking dish. Top with the mashed potatoes, covering the entire dish and sprinkle with cheddar cheese.
Place the baking dish in the preheated oven and cook for approximately 25 minutes, or until bubbling and the cheese is completely melted.