Coat a medium saucepan with cooking spray; place over medium-high heat until hot.
Add green onions and garlic; saute until tender.
Add milk and next 3 ingredients; cook over medium heat, stirring constantly with a wire whisk, until mixture is thickened and bubbly.
Remove from heat.
Beat egg yolk in a medium bowl. Gradually stir about one-fourth of hot cornmeal mixture into egg yolk; add to remaining cornmeal mixture, stirring constantly with a wire whisk.
Beat egg white at high speed of an electric mixer until stiff peaks form. Fold one-third of egg white into cornmeal mixture; fold in remaining egg white.
Pour mixture into a 2-cup casserole coated with cooking spray.
Bake at 375 for 35 to 40 minutes or until puffed and golden.
