In 12-inch skillet, melt butter over medium-high heat. Cook mixed vegetables and onion in butter 5 minutes, stirring occasionally, until softened. Add flour, 1/2 teaspoon of the tarragon, the salt and garlic powder; stir to combine. Cook 1 minute. Stir in broth and whipping cream. Cook 5 minutes, stirring constantly, until sauce thickens. Stir in chicken. Pour into baking dish.