Mix butter with powdered sugar until blended.
Add sour cream and vanilla sugar.
Mix all together.
Add flour slowly and using the flat beater attachment mix all together until all combined.
Remove the dough from the bowl and knead by hand on a floured surface.
If too soft, add more flour. Need to be able to roll out thin, approx 3-4mm thickness and measuring about 10" x 13" in size. Trim away the uneven edges to make an even rectangular shape.
Divide into 3 wide strips, approx. 3" wide each.
Use jam at room temp and spread down the center of each strip. You can also use a piping attachment.
Pinch together both sides of the 3" strip to enclose jam inside and then gently roll to make smooth rounded edges.
Lay the prepared pieces on a parchment paper lined baking tray.
Cut into desired lengths, approx, 1”long.
Bake for 17min at 360F.
Remove from the oven and keep on the tray until they cool.
Mix powdered sugar with vanilla sugar and sift over top of cooled cookies.