In a medium saucepan cook potatoes and carrots, covered, in boiling water about 12 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 1/2 cup of parmesan cheese, green onion, and sour cream or yogurt. Transfer to a 1-quart 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.