For making the crust, in a large bowl, mix together the flour, salt and sugar. Add the butter to the bowl and using a pastry cutter, cut through the mixture working your way through it. It should resemble the texture of sand after a little while.
Add water to the bowl and knead till the dough comes together.
Flatten the dough to a ½ inch disc. Fold it over itself several times and flatten to form layers. Divide it into 2 equal pieces. Shape them into discs and cover in a plastic film. Refrigerate for a good 6 hours.
In a large bowl, combine berries, sugar, salt, plums and vanilla and set aside. Drain all the extra liquid, sprinkle with cornstarch and mix well.
Pre-heat the oven to 400 degrees, grease an 8-inch pie plate. Rest the dough for 15 minutes before you roll them out. Roll the first half into a 15-inch disc. Lift the crust carefully and set t into the pie plate. Pour the fruit mixture and gently event it out.
Roll the second half of the dough into a rectangle and cut ½ inch wide strips. Place the strips on top of the pie working your way through the whole surface. Weave the remaining strips of dough forming a lattice. Trim the edges and crimp the edges using your thumb creating a rim. Chill the pie for 15 minutes.
Bake for 20 minutes in the pre-heated oven. Lower the temperature to 350 degrees and bake for another 1 hour 15 minutes. Remove the golden, bubbly pie out of the oven and let the pie cool completely before serving!