In a medium saucepan cook potatoes and carrots, covered, in boiling water about dozen minutes or until carrots are tender. Meanwhile, in a small skillet cook bacon until crisp. Drain, crumble and set aside. In a large mixer bowl mash potatoes and carrots with a potato masher or an electric mixer on low speed. Gradually beat in the milk till mixture is creamy. Stir in eggs, the half cup of parmesan cheese, green onion, and sour cream or yogurt. Transfer to a 1 litre casserole. Bake, uncovered, in a 350` oven for 20 minutes. Sprinkle with the bacon and 1 tablespoon parmesan cheese. Bake for 15 minutes more or until center is set.