There are recipes with sour cream and some with vodka. I like the vodka ones because the flake is a bit better.
I have had the most success using the food processor full of wheat and slowly adding frozen butter to create a powder that just barely clumps together when pressed. Then add the vodka, it gets stickier, you roll it out into sheets and refrigerate.
And, because I add cardamom to everything I bake, I add just a bit to the flour.