Preheat the oven to 350 degrees.

Place the unbaked pie crust in a 9 inch deep dish pie pan. Pinch the edges to create a scalloped appearance or decorate the edges to your preference.

Pour the blackberries into the unbaked pie crust.

In a mixing bowl, whisk together the sugar, flour, and cinnamon with the heavy cream. When this mixture is well combined, pour it over the blackberries, making sure all the blackberries are evenly covered.

Bake the pie at 350 degrees for about one one hour, covering the edges of the crust with aluminum foil or a pie shield about half way thru the baking time to keep the crust from over-browning. You can tell your pie is done when the edges have slightly puffed and the center slightly wobbles when you move the pie.

Remove the pie to a wire rack to cool completely. Then refrigerate and allow the pie to chill completely before serving.