Preheating the oven to 350° F. In a medium-sized cast iron skillet, toss berries with sugar, flour, cornstarch, lemon juice, and salt.
Stir until mixed and spread flat in the skillet Set aside.
Lattice Crust
Using a food processor, pulse flour, salt, sugar, and cold butter. If the dough is very dry and crumby, add the water and continue pulsing.
Heavily grease two large pieces of wax paper. Place the dough between both pieces of wax paper and flatten. Set on a large plate or baking pan and let chill in the fridge for 10-15 minutes.
Remove from the fridge and flatten into a large circle with a rolling pin. Using a pizza cutter, cut the dough into wide strips. Return to the fridge for 10 minutes to chill.
Lay out the dough strips in a lattice pattern across the top of the berry mixture. Brush the crust with egg wash.
Bake for 45 minutes. Rotate 180° degrees and continue baking 20-30 minutes until the crust is golden brown. Serve with ice cream or whipped cream!