Begin by chopping the butter into 1-inch cubes and placing them in the freezer for 5 minutes to ensure it's nice and cold.
To a large bowl, add the flour, and salt and mix them together. Add the cold cubes of butter to the flour.
Use a pastry cutter to cut the butter Into the flour roughly, but not too small. A few small pieces are fine, but the rest can be left in fairy large chunks. If the butter is melting at any point, place the bowl in the refrigerator.
Add the lemon juice or vinegar to the ice-cold water. Drizzle it slowly into the flour mixture, a few tablespoons of water at a time. Use a spatula or your hands to combine it into a shaggy dough, and add in enough water as needed but not too much. Add any extra water in slowly, a tablespoon at a time.
It should hold together easily when pressed but not be sticky. If the dough is super crumbly, add a bit more water. You don't want it sticky. Form the dough into a mound and let it chill in the fridge for 10 minutes. If your room temperature is very cold, you can begin rolling immediately.
On a floured work surface, roll the dough with a rolling pin into an 8x12-inch rectangle. You will see large chunks of butter in the dough. Dust off any excess flour from the top of the dough.
Fold the bottom third of the dough up to the middle, then fold the top third over the top to make a pamphlet shape. That was Fold 1. Turn the dough a quarter turn, roll it back into a rectangle, and repeat the folding. That was fold 2.
Repeat this process three more times so you do 6 folds in total. You can trim the edges of the dough to neaten them when folding to make the lamination more even.
If you are making this on a cold day, then there is no need for any fridge rest in between the rolling of the layers unless the butter is melting. The rough puff pastry will likely need a fridge rest in between every second fold to ensure the butter stays chilled in the summertime.
After the last fold, wrap the dough up tightly in cling film and place it in the fridge for at least 2 hours or up to 24 hours. It can also be portioned and frozen for up to 3 months. See the above post for freezing instructions.