Step 1

In 3-quart saucepan, melt butter over medium heat. Add onion; cook and stir until tender. Reduce heat to low. Stir in flour, mustard and pepper; cook and stir until mixture is smooth and bubbly.

Step 2

Gradually stir in milk and broth. Stir in frozen vegetables and marjoram. Heat to boiling over medium heat, stirring occasionally. Reduce heat to low; cover and simmer 3 to 5 minutes or until vegetables are crisp-tender.

Step 3

Add cheese and tuna; heat, stirring gently, until cheese is melted.