In a small bowl, add an egg and break it up with a fork. Add the vinegar and the cold water. Set it in the fridge or freezer for a moment. It needs to be kept cold. You can also add a couple ice cubes to keep it cold, but reduce the water amount slightly.
In a bigger bowl or your mixer, add the flour, salt, baking powder and chopped fresh herbs. Cut the cold butter into small chunks which makes it easier to break apart and incorporate into the flour.
Then add the butter to the flour mixture. If using a pastry cutter, break up the butter and keep cutting and mixing until the butter and flour resemble small peas. If using a mixer, pulse in your mixer till it resembles small peas.
Make a well and add the liquid. Using a fork or your fingers, mix the liquid with the flour and butter gently slowly and mix till just combined. If using a mixer, just pulse quickly until the dough comes together. It its fine if it looks like a shaggy dough. As it rests, the moisture will distribute itself.
Pour out on to a surface and mold into a ball. Wrap it in plastic wrap and place in the fridge for at least 1/2 an hour. 1 hour is better.