01 - In a large bowl, whisk together flour, salt, and sugar (if using). Add cold butter cubes. Using a pastry cutter or your fingertips, work the butter into the flour until the mixture resembles coarse crumbs with pea-sized pieces. Gradually add ice water, starting with 1/4 cup, mixing gently until the dough just comes together. Add more water if needed. Do not overwork. 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 the left over the new middle. After one set, start the fishtail: Take the outermost right strip and cross it to the center, then the outermost left to the center, always pulling from the outside. Continue until complete; press ends together. Repeat for additional braids as needed to cover your pie edge.
04 - Trim any excess dough from the filled pie. Brush edge lightly with water to help the braid stick. Gently lift and shape braid(s) around the 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 the crust with braid for 15 minutes, then bake at 375°F for 12-15 minutes until golden.