In medium bowl, combine eggs, milk, salt and nutmeg; beat well.
In 10-inch skillet over medium heat, melt butter. Saute onion until tender. Reduce heat to low; add egg mixture to skillet. Cover; cook over low heat for 6 to 8 minutes or until mixture is set.
Arrange asparagus in center of frittata. Sprinkle carrots around edge. Sprinkle cheese over asparagus, cover; cook 2 to 4 minutes or until cheese is melted. Let stand 5 minutes before serving.