Preheat oven to 375°F. Coat 2-quart ovenproof dish with cooking spray.

In large saucepan, melt 3 tablespoons butter oven medium-high heat. Remove pan from heat; stir in flour. Return to heat and continue to cook until the mixture becomes lightly browned, about 3 minutes. Add 1/4 teaspoon salt and 1/4 teaspoon black pepper. Set aside.

While sauce is cooking, melt remaining tablespoon of butter in large skillet. Add mushrooms, onion and carrots and cook for about 10 minutes over medium-low heat, until lightly browned. Add chicken meat; cook 2 minutes. Add artichoke heats; stir together well. Pour in thickened broth sauce; bring to a simmer and cook 10 minutes. Stir in tarragon. Add remaining 1/2 teaspoon salt and 1/4 teaspoon pepper.

Pour chicken mixture into prepared dish. Place pastry dough over top; trim ends to fit sides of dish. With knife, lightly score pattern on top. Bake in preheated oven 30 minutes or until top is golden brown. Cool slightly before serving.