Line 9 inch pie pan with half the pastry. Cover and chill. Combine blackberries, flour, spices and sugar together in another mixing bowl. Spoon into pie shell.
Cover with remaining pastry. Cut steam vents. Bake in 450F degree oven for 15 minutes. Reduce oven temperature to 350F degrees. Bake 34 to 40 minutes longer or until browned.
Meanwhile, add cream and 3 lemon verbena leaves to a small saucepan. Heat cream over medium-high heat, only at a simmer for 5 minutes. Pour cream and verbena leaves into a glass container and chill for 20 minutes.
Remove verbena leaves from cream. Pour cream into the chilled bowl and whip using an electric mixer. Add sugar to taste.