1) Make the biscuits: in a medium bowl, combine Bisquick, polenta, garlic powder and cheese. Stir in buttermilk just until dry ingredients are moistened. Set aside.
2) Make the pot pie: preheat oven to 180 degrees C. Lightly grease 4 (450 ml) oven safe bowls. Place bowls on baking pan.
3) In a large skillet, melt butter over medium heat. Add onion, celery, mushrooms and cook 6 to 8 minutes, or until vegetables are tender, stirring occasionally. Stir in flour and cook 2 minutes, stirring constantly. Stir in Creole seasoning, sherry and cheese. Stir in single cream, and cook 5 minutes, or until thickened. Remove from heat and add shrimp, scallops and crab. Spoon into prepared dish.
4) Spoon the drop buttermilk biscuits evenly over each casserole. Bake for 20 minutes or until biscuits are golden.