DEFROST VEGETABLES, if necessary. Roughly chop them into 1/4-inch pieces and set aside on a plate. Heat the oil in a large skillet over medium heat, add the onion and cook, stirring, for 5 minutes. Decrease heat to low and add the vegetables. If using uncooked ones, cover and cook for 10 minutes. If using cooked ones, cook uncovered for 5 minutes. Stir in the flour and add the milk. Cook, stirring, another 2 minutes or until mixture thickens. Add the salt and pepper. Remove the skillet from the heat, add the egg, salt, pepper and rosemary and scrape the mixture into a bowl to cool. Stuffing can be stored, covered, in the refrigerator for up to 7 days. To freeze, place 1-cup amounts of stuffing in airtight freezer bags or containers, label and place in freezer for up to 3 months.