Preheat your oven to 400°F (200°C) and line a rimmed baking sheet with parchment paper to catch any spills. Gently unroll one pie crust and press it lightly into the bottom and up the sides of a 9-inch pie dish.

In a large mixing bowl, combine the Saskatoon berries, granulated sugar, cornstarch, lemon juice, almond extract, and ground cinnamon. Toss the mixture gently with a spatula until the berries are evenly coated and no dry cornstarch remains.

Pour the berry filling into the prepared pie crust, spreading it out into an even layer. Dot the top of the berry filling evenly with the small cubes of unsalted butter to add richness to the filling.

Place the second pie crust over the filling. Trim the overhanging dough to about half an inch, then fold the top crust under the bottom crust and crimp the edges with your fingers or a fork to seal the pie completely.

In a small bowl, lightly beat the egg with a splash of water, then brush this egg wash evenly over the top crust. Use a sharp knife to cut 4 to 5 small slits in the center of the pie to allow steam to escape during baking.

Sprinkle the coarse sugar evenly over the egg-washed crust for a sweet, crunchy finish. Place the pie on the prepared baking sheet and bake for 20 minutes at 400°F (200°C).

Reduce the oven temperature to 350°F (175°C) and continue baking for another 25 to 30 minutes, or until the crust is deep golden brown and the thick berry juices are bubbling through the slits.

Remove the pie from the oven and let it cool completely on a wire rack for at least 2 hours so the filling can set properly before slicing. Serve warm or at room temperature with a generous scoop of vanilla bean ice cream.