Melt the butter in the olive oil in a large heavy pot over low heat. Add the onion and cook, stirring, until soft, 5 minutes. Add the garlic and cook for another 3 minutes. Sprinkle with the flour, stir, and cook to form a paste, 1 minute longer.
Stir in the carrots, potatoes, broth and cream. Increase the heat to medium and bring to a boil. Reduce to medium-low and simmer, partially covered, until the vegetables are tender and the sauce has thicked, 20 minutes. Add the peas, corn, tomatoes, tarragon, orange zest and lobster. Simmer for 5 minutes to blend the flavours. If the mixture is too thick, add 2 more tablespoons broth. Season with sald and pepper and set aside.
Preheat the oven to 350°F.
Beat the egg and 1 tablespoon water together in a small bowl. Place 1 1/2 cups of the lobster mixture in each of four individual (13.5 oz.) souffle dishes.
Lay a sheet of puff pastry on a lightly floured surface and roll it out 1/8 inch thick. Cut four rounds of puff pastry, each 2 inches larger than the diameter of the souffle dishes. Brush the egg wash over the inside and outside rim of the souffle dishes. lay the pastry over the top of each dish, trim the overhang to 1 inch, and crimp the edges around the rim to form a tight seal. Cut several slits in the center of the pastry to allow the steam to escape and brush it with the remaining egg wash.
Place the dishes on a baking sheet and bake until the crust is golden and puffed, 40-45 minutes. Serve immediately, garnished with the tarragon sprigs.
NOTE: Generally a 1-1/2 pound lobster will yield 1 cup of meat.