In a medium bowl, mix together flour, salt, and sugar. cut in butter using a pasty cutter, two forks, or your fingers (I prefer to use very cold butter, chopped it with a knife
, and then mix it into the flour by hand). Incorporate butter until mixture is the consistency of thick crumbs. Add egg, vinegar, and 4 tbsp cold water. Mix with a fork and form into a ball. (I ended up adding 2 more tbsp water as the dough was dry and not coming together for me, 6 tbsp was perfect).