All ingredients should be gathered. Pre-heat the oven to a temperature of 425 degrees F (210 degrees C).
In a large bowl, combine 3 1/2 cups blackberries and 1/2 cup of sugar with flour. Pour the mixture into a pie crust that has not been baked. Spread the remaining 1/2 cup of berries over the sweetened berries.
Cover with top crust. Seal and crimp edges and cut vents into the top crust to allow steam to escape.
Sprinkle the remaining 1/4 cup of sugar on top and brush with milk.
Bake pie for 15 minutes in a preheated oven. Bake for 20-25 minutes at 375 degrees F. Cool on wire rack.
Enjoy and serve!