Add 2 T olive oil to pan over medium heat, add leeks and cook 10 minutes. Add chicken and sausage and cook until lightly browned and remove from the pan. Add 3 T butter and 2 T olive oil and flour, cook 1 minute, then add broth, milk, parsley, chives, tarragon and salt & pepper to taste. Set aside 3/4 c sauce. Add back in the chicken mixture to remaining sauce and turn off.
Roll out 2/3 of the pastry crust into a pie pan. Spoon in mixture. Roll out remaining crust and cut into strips and place over pie.
Bake at 425 for 20-25 minutes and serve with remaining sauce.