01 - In a large bowl, whisk together flour, salt, and sugar if using. Add cold butter cubes and work into the flour using a pastry cutter or fingertips until mixture resembles coarse crumbs with pea-sized pieces. Gradually add ice water starting with 1/4 cup, mixing gently until dough just comes together. Add more water if needed without overworking. Divide dough in half, flatten into disks, wrap in plastic, and chill for at least 1 hour.
02 - On a lightly floured surface, roll one chilled disk into a rectangle about 1/8 inch thick. Using a ruler and knife or pizza cutter, cut at least 6 even strips about 12 inches long and 1/2 inch wide.
03 - Lay three strips side by side with ends pressed together. Begin a regular braid by crossing the right strip over the middle, then left over the new middle. After one set, start the fishtail: take the outermost right strip and cross to center, then outermost left to center, always pulling from outside. Continue until complete and press ends together. Repeat for additional braids as needed to cover pie edge.
04 - Trim excess dough from filled pie. Brush edge lightly with water to help braid stick. Gently lift and shape braid(s) around pie rim, pressing lightly to adhere. Brush braid with egg wash for shine.
05 - For filled pies baking longer, add braid before baking. For pre-baked shells blind baking, chill crust with braid for 15 minutes, then bake at 375°F for 12-15 minutes until golden.