Using a pastry blender, cut the butter into the flour until the combination is crumbly with pea sized bits.
Add the sour cream and knead the mixture on a floured board. Pat the dough, once it's kneaded together into a square, about 6x6 inches in size. Wrap up and chill at least 3 hours or all night.
Layer half of the sugar onto a cutting board or the rolling area, and place half the dough down on the sugar and roll out till it is a 10 to 12 inch square. Using a butter knife, lightly crease the dough down the middle, making a straight line.
Roll the dough up firmly starting on one side and roll it towards the center. Do the same on the other side. Try to "grab" as much sugar onto the dough as you can. Squeeze dough together to make it tight like the palmiers should look. Chill for 3 or more hours.
Do this with the other half of dough as well with the rest of the sugar.
Cut the roll of dough into slices about one-fourth inch thick with a sharp knife and bake the cookies on an un-greased baking sheet leaving room to grow between cookies.
Bake about 8 to 10 minutes, then turn the cookies over and bake for 5 minutes longer. The cookies should be brown and caramelized.