Use your food processor, this makes things so much easier.
In a bowl mix the flour and salt, whisk well.
Cube the butter but keep it in the refrigerator until ready to add to the dough.
Add the flour mixture to the food processor bowl. Add ¾ cup of the butter and the pulse. Pulse about 12-14 times until you had a sandy grainy appearance of the dough.
Add the other ¾ cup of butter and pulse about 3 times.
Add the cold water and pulse about 5 times.
Empty the dough onto a flat clean floured surface and knead. Do not overknead or you will ruin the dough. Knead about 20-30 seconds until you have a dough ball. You will see pieces of butter in the dough, this is fine, don't worry.
Roll out the dough using a rolling pin to about 12 x 18 inches. Fold it over twice, cover with plastic and place in the refrigerator. Leave this for at least 2 hours. You can vacume pack and freeze the dough. It will keep for months this way. Just freezing it will keep for about a month.
Your dough is finished once it has set in the refrigerator. Roll out as indicated above in the galette recipe.