Place flour in a food processor. Add salt and sugar and process for 20 seconds to combine. Stop machine. Add chunks of butter / shortening on top of flour. Process by pulsing intermittently to break the fat into the flour (until you have a crumbly mixture).
Drizzle water and lemon juice on top and turn machine on for 15 seconds (no more) until the mixture holds together more or less).
Turn dough out onto a lightly floured board. Knead very gently for a few seconds to smooth out dough. Pat into a flattened disc and wrap well in plastic. Chill dough at least 1 hour or overnight before using. This dough can be frozen for up to three months.
Notes: You may also use 1/2 butter and 1/2 unflavored shortening.