Preparation:
Cook M&M California Style Mixed Vegetables in large pot of boiling water or in microwave, until tender crisp. Drain vegetables and keep warm.
In large saucepan, melt butter over medium heat. When bubbly, stir in flour; cook, stirring constantly, for 2 minutes. Gradually stir in milk; continue stirring until mixture thickens and bubbles. Reduce heat and simmer for 1 minute.
Stir in old cheddar cheese until smooth. Stir in mustard. Season with salt and pepper.
Pour cheese sauce over vegetables.