Melt butter in a large nonstick skillet over medium-high heat. Add leek, shallot, and thyme; sauté 2 minutes. Add potatoes; sauté 2 minutes. Add wine; cook 1 minute or until liquid evaporates. Stir in mustard and broth; bring to a boil. Cook 4 minutes, stirring occasionally. Stir in chicken, mixed vegetables, salt, and pepper; cook 1 minute. Combine cornstarch and 2 tablespoons water in a small bowl, stirring with a whisk. Add cornstarch mixture and half-and-half to pan. Reduce heat, and simmer 2 minutes, stirring constantly. Spoon mixture into a 13 x 9-inch baking dish coated with cooking spray.
Lightly spoon baking mix into dry measuring cups; level with a knife. Combine baking mix, milk, and egg in a medium bowl, stirring with a whisk. Spoon batter over chicken mixture; spread evenly to cover. Bake at 425° for 20 minutes or until topping is golden and filling is bubbly. Let stand 10 minutes.