Whisk the flour, salt and sugar together in a large bowl. Add the chilled butter cubes and cut them into the flour mix using a pastry blender or your fingers. Work quickly and cut the butter into the flour until mostly pea sized pieces of butter remain (don't overblend – you want a few bigger chunks of butter left intact). If the butter starts to get a little melty just put the whole bowl in the freezer for 5 minutes to chill it out (you want everything to stay super cold for flaky pastry!).
Combine the water, vinegar and ice in a bowl. Sprinkle 2 tbsp. of the ice water mix over the butter‐flour mix and cut it in with a bench scraper or spatula until combined. Continue to sprinkle over 1–2 tbsp. of the ice water and cut it in until the dough starts to clump together in shaggy bits. You want the bits of dough to be able to just hold together when pressed together between your fingers. Some dry bits at the bottom of the bowl are fine, if there a lot though, just keep adding 1–2 tbsp. of the water until there are less dry bits. Gently press the shaggy bits of dough together with your fingertips and shape into a ball, try not to overwork the dough or warm it up too much. Cut the ball in half, re‐shape each piece into a round, flat disc and wrap each in plastic wrap. Place in the fridge for at least 1 – 2 hours to chill (if it still isn't super chilled before rolling out, let it have some time in the freezer for about 15 mins).
Remove one pastry disc from the fridge, this first disc will be your base. Roll it out on a floured surface until it's about 7cm / 3 inches larger than the pan you're using and about 3 mm / 1/8 inch thick. Fold the rolled out dough in half and lay it across one side of a buttered pie dish, positioning the fold in the center. Unfold the dough and gently fit it into the pan, pushing it carefully into the edges so that there are no gaps between the pastry and the pan. Do not pull or stretch the dough. Cover the crust with plastic and refrigerate for at least 30 minutes, preferably 1 hour or more, and tightly wrapped up to 3 days before using.
Remove the other pastry disc from the fridge, this is for your lattice. Repeat the rolling out of the dough as per the first piece of pastry, however this time after rolling, trim the left and right side of the dough a little to create straight edges, then cut the dough (from top to bottom) into 8–10 strips, depending on how thick you want your lattice pastry strips to be. Place the strips on a parchment lined, floured baking tray and rest, covered in plastic, alongside the pastry lined pie dish.