Heat oven to 375°F. In 12-inch ovenproof skillet, melt butter over medium-high heat. Add onions, carrots, celery, salt and pepper; cook 5 to 7 minutes, stirring frequently, until tender. Stir in flour; cook 1 to 3 minutes or until beginning to brown. Gradually stir in broth and milk, cooking and stirring 1 to 3 minutes longer, until bubbly and thickened. Stir in chicken and peas. Remove from heat.