Place 1 1/4 cups of the milk in large nonstick saucepan; place over medium-high heat. In small bowl, combine remaining 1/4 cup milk and flour; blend with wire whisk until smooth. Add to milk in saucepan; cook about 5 minutes, stirring constantly, until thickened.
Add onion, pepper and Worcestershire sauce; mix well. Bring just to a boil. Reduce heat; simmer 10 minutes or until onion is tender, stirring occasionally.
Stir in cheese until melted. Add spinach; mix well. Cook until thoroughly heated. Serve with slices of baguette-style French bread or cut-up fresh vegetables.