In a high speed blender or food processor, add your flour, powdered sugar, salt, and chopped butter. Blend well, until the butter has been broken up into tiny pieces.
Slowly add the iced water in, 3 tablespoons at a time. Mix after each time. Once large clumps appear, stop adding water.
Lightly flour a flat surface. Transfer the dough onto it. Gently press and knead the dough, until the butter is no longer clumpy and the dough is smooth. Form into a ball and divide it into two pieces. Gently flatten it out until an inch in thickness. Wrap the dough and refrigerate it for an hour.
When ready to make the pie, roll out the dough and evenly, and place one of the balls of dough into the 8-inch pie pan. With the second piece of flattened dough, cut thin lines, and set aside.
Making the blueberry pie filling
In a large mixing bowl, mix the sugar with cornstarch until combined. Add the blueberries and pour the lemon juice on top. Mix well, until fully incorporated.
Assembling and baking the pie
Preheat the oven to 180C/350F.
Pour the blueberry pie filling into the pie crust, ensuring none of the juice touches the sides. With the strips of dough, place in a criss-cross shape over the top of the entire pie. If desired, brush the tops of it with melted butter, or milk.
Bake the pie for 50-60 minutes, until golden on top. Remove from the oven and let sit for 10 minutes, before slicing and serving.
* Vegan butter must be chilled. Use vegan butter from a block, if possible. ** You may need less or more, depending on the quality of your butter. *** White sugar, uncut sugar, and even coconut sugar can be used. You can also make this with a keto pie crust.