Combine flour and salt in one bowl and the butter in another bowl. Place both bowls in the freezer for 1 hour.
Remove the bowls from the freezer and make a well in the center of the flour. Add the butter to the well and using a pastry blender cut it into the flour until the mixture resembles coarse meal. Make another well in the center of the mixture .
In a small bowl whisk together the sour cream, lemon juice and water. Pour half the mixture into the well. Using your fingers mix everything until large lumps form. Remove the large lumps and repeat with the remaining liquid and flour-butter mixture. Pat the lumps into a ball and DON'T OVERWORK THE DOUGH! Divide the dough into two portions, cover it with plastic wrap and refrigerate for (at LEAST)1 hour. And if you want to make the pastry ahead of time, it can be refrigerated overnight.
The ingredients can be halved to use for a one crust pie or galette.