Melt margarine in 1-quart saucepan over low heat. Stir in flour, salt and garlic. Cook over low heat, stirring constantly, until mixture is smooth and bubbly; remove from heat. Mix milk and egg yolk until smooth; stir into flour mixture. Heat to boiling, stirring constantly. Boil and stir 1 minute. Stir in broccoli mixture; remove from heat.