In a large sauce pan, such as a Dutch oven, cook pasta in boiling water 4 minutes. Add asparagus; cook 2 minutes or until tender. Drain.
While the pasta cooks, melt butter in a large skillet over medium heat. Add onions and lemon zest; sauté 1 minute. Add juice; cook 1 minute or until liquid almost evaporates.
Combine milk and eggs in a small bowl; stir well with a whisk. Add pasta mixture and milk mixture to skillet; stir well. Cook over low heat 3 minutes or until milk mixture is slightly thick, stirring constantly (do not boil). Stir in dill, salt, and nutmeg. Serve immediately.