In a large , deep skillet, heat 2 tablespoons of oil over medium heat. Add chicken ,cook,stirring occasionally, until golden,(5 minutes). transfer chicken to a plate.
In the same skillet, heat remaining oil over medium heat. Add shallots and garlic, cook, stirring frequently, for 2 minutes. Add onion and leek; cook, stirring occasionally for 5 minutes.
Add mushrooms,carrots, and celery. Cook stirring occasionally for 5 minutes
Mix together broth, cream, and flour. Pour cream mixture into skillet. Cook, stirring frequently,until mixture just thickens, 10 minutes. Return chicken to skillet,stir in alt and pepper. Spoon into a large deep casserole
Preheat oven to 400 degrees F. To prepare topping , in a medium bowl, mix together flour, baking powder, and salt. Using a pastry blender or 2 knives, cut butter into flour mixture until coarse crumbs form
Mix together parsley and milk. Make a well in center of flour mixture. Add milk mixture all at once to well. tossing with a fork until a soft dough forms.
Drop dough by heaping tablespoons on top of chicken mixture, 1/2 inch apart.
Bake casserole until topping is golden and filling bubbles, about 20 minutes. Transfer to a wire rack to cool slightly. Garnish with green onion strips