Step 1

Preheat the oven to 425 degrees F (220 degrees C).

Step 2

Remove all wrapping from the pastry shells and set on an ungreased baking sheet. Bake in the preheated oven until golden brown and puffed, about 20 minutes (follow directions on package).

Step 3

Melt 1 tablespoon butter in a large skillet over medium-high heat. Add bay scallops, and saute quickly on both sides until lightly browned, about 2 minutes per side. Do not overcook. Remove scallops from skillet and set aside.

Step 4

Reduce heat to medium, and melt remaining tablespoon butter. Add mushrooms and shallots, and sautè until just tender, 3 to 5 minutes.

Step 5

Whisk half-and-half and flour into the skillet, whisking until thickened; add white wine, sherry, lemon juice, and Dijon mustard, and whisk into the cream sauce.

Step 6

Stir in Parmesan cheese, 1 tablespoon tarragon, and pepper. Return scallops to the cheese sauce, stir, and reheat briefly.

Step 7

Remove top of the puff pastry shell, and fill with cheesy scallops, overflowing slightly to serve. Garnish with additional fresh tarragon if you like.