Beat the room-temperature butter with the powdered sugar using a whisk until smooth, then pour in the vegetable oil and mix again.

Add the vanilla essence and baking powder, then gradually stir in the flour and knead the dough.

Pinch off a piece of dough the size of two walnuts and mix in the cocoa and sour cream - this becomes the chocolate dough.

On a floured surface (ideally between sheets of plastic wrap), roll the white dough into a sheet. Pinch off pieces of the chocolate dough, roll them into ropes, and arrange them on top.

Cover with plastic wrap and roll together so the pattern presses into the sheet. Remove the wrap, cut into pieces, and place on parchment.

Bake in a preheated oven at 170°C for 15-20 minutes. Let the cookies cool. Enjoy!