Brown 1/2 pound sausage in a skillet with 1/4 cup chopped onion and 1 each diced celery stalk and carrot. Add 1/2 cup mashed potatoes, and salt and pepper. Roll out a can of refrigerated biscuit dough and cut into twelve 3-inch rounds. Top each with a spoonful of meat filling and fold in half; pinch to seal and brush with a beaten egg. Make slits in the top and bake at 350 degrees F until golden, about 15 minutes.