Preheat the oven to 400 degrees F. Place a baking sheet upside down on the lower oven rack. Line another baking sheet with parchment paper.
Wash 3 cups fresh blackberries, then blot them dry with a paper towel.
In a large mixing bowl, add the blackberries, zest of 1 lemon, 1 tablespoon lemon juice (about half a lemon), 1/4 cup granulated sugar and 1 tablespoon cornstarch. Gently mix the ingredients, taking care to keep the blackberries mostly intact.
Lay 1 refrigerated pie crust out on the baking sheet you prepared earlier. Spoon the blackberry mixture into the center of the pie crust leaving a 2 inch border around the edge.
Starting at the top, fold the the pie crust inwards so that it is touching the edge of the fruit, keep folding as you move around the pie crust overlapping as you go. Gently press the pie crust on the overlapping areas to secure it.
Brush the pie crust with 1 egg yolk, beaten and scatter over 2 tablespoons turbinado sugar (coarse sugar).
Place the baking sheet on top of the upside down preheated one and bake for 35 minutes or until the pie crust is golden brown and the blackberries are bubbling.
Remove from the oven and allow to cool for a few minutes before slicing and serving with ice cream. Enjoy!