Mix milk and mustard in a bowl. Mix cheese with flour and chives in another bowl. Dip chicken breasts into milk mixture, brushing with brush to coat evenly. Dip breasts into cheese mixture, pressing to coat all sides. Place on a cookie sheet, putting extra cheese on top of the chicken. Bake at 400" for 30-35 minutes. Serve hot with twice baked potatoes and or a cold salad.