Preheat oven to 350°F.
Rinse scallops and cut in half. Simmer scallops, milk and thyme in heavy saucepan or Dutch oven over medium heat for 10 minutes. Remove scallops from liquid and set aside, reserving liquid.
Melt butter in same saucepan or Dutch oven over medium heat; add mushrooms and cook for 5 minutes. Add flour and cook, stirring constantly, for 1 minute. Gradually whisk in reserved liquid, sherry and TABASCO® Green Sauce, stirring constantly until thickened. Stir in onion and scallops. Spoon into 9-inch pie plate; top with mashed potatoes, spreading them to edge of pie plate to seal. Bake for 25 to 30 minutes, until potato crust is golden brown.
Makes 6 servings.