In a medium bowl, whisk together flour and salt. Cut the cold butter into small cubes and add to the flour. With you fingers, rub the butter into the flour until no clumps of butter remain. Dough will still be very dry and crumbly.
Add ⅓ cup of the ice water (but just the cold water, no ice) to the dough. Mix with your hands or a spatula until dough is very combined, and kneed for a minute while still in the bowl. The dough is very sticky and wet, but shouldn't be runny. Don't add any flour, the dough is supposed to be sticky.
If you are making a large galette (about 12" x 18") form the dough into one large ball and wrap in plastic. If you would like two smaller galettes (about 9" rounds), divide the dough into two equal balls and wrap in plastic. Refrigerate for a minimum of 30 minutes. The more firm the dough is, the easier it is to work with.
Once dough is firm, roll out to your desired shape on parchment paper, keep them on the parchment throughout the baking process. These are rustic tarts, so you do not need to have perfect edges, just the general shape. Roll the dough about 1/8" - 1/16" , don't go any thinner or the dough will tear. If the dough becomes too sticky at any point, stick it back in the fridge for 10-15 minutes.