Add the butter to the flour mixture and cut it in using a pastry blender or a processor. The butter should still be visible as small pea size lumps in the dough.
Stir in the sour cream. The dough will be a shaggy mixture that does not hold together.
Turn the dough out on a floured counter or pastry mat and knead it until it comes together in a ball.
Shape the dough into a log and roll it out into a 8”x10” rectangle.
Dust the dough with flour and fold it in three folds, like a letter going into an envelope.
Turn the dough 90 degrees and roll it out into another 8”x10” rectangle. Fold it like a letter again.
Wrap the dough in plastic wrap and refrigerate for 30 minutes or up to overnight.
Make the Palmiers
Take the pastry out of the refrigerator. If it has been chilling for more than 30 minutes, let it rest until it is cool and pliable, 15-30 minutes.
Sprinkle sugar all over your pastry board. Place the dough on top of the sugar and liberally sprinkle sugar over the dough.
Roll the dough into an 11”x14” rectangle. While you are rolling the dough, sprinkle sugar under it and on top to keep it from sticking.
Once the rectangle is formed, start to roll it tightly, alternating sides as you roll. After each turn, sprinkle more sugar on top of the roll. The two rolls of pastry dough should meet in the middle.
Wrap the dough tightly in plastic wrap and refrigerate for 30 minutes to 2 hours.
Preheat your oven to 375 degrees.
Line two baking sheets with parchment paper.
Slice the chilled dough in ½” slices. Carefully dip the slices into some sugar, making sure to get all the sides and edges.
Bake the cookies on the prepared sheets, 3” apart, for 14 minutes. The edges should be evenly browned.
Now carefully flip the cookies over and continue baking for an additional 6 minutes. Watch them to make sure they don’t burn.