Put the flour and salt in a 3-quart bowl, and stir to blend. Scatter the butter slices over the flour, and cut in with a pastry blender until the mixture consists of particles that vary in size from small peas to bread crumbs. Stir in the sour cream with a fork. The pastry will appear dry because the sour cream is thick and does not disperse easily. With your hands, manipulate dough into a ball. Divide dough as recipe directs. Wrap in plastic and refrigerate until cold and firm, at least 4 hours and up to 3 days. The dough can be frozen for up to 1 month.month.