Method

• Pre-heat the oven to 350 degree F.
• In a bowl, mix the flour, sugar,salt and Add soft butter to make soft dough
• Divide the dough into two equal parts.Take one part of dough and add vanilla extract.Mix well.
• Now take second part of dough and add cocoa powder.Mix well again.
• Keep both dough in refrigerator for half an hour.
• After half an hour,Take the both dough and roll out into flat rectangles of 1/4" thickness on a plastic sheet( trim the edges to make them into equal sized rectangles).
• Now place the chocolate layer on top of the vanilla layer showing just 1/4" of the vanilla layer on top(This will help you get a clean swirl when you roll it)
• After placing it, gently start rolling the layers until you form a log and press the dough on three sides to get triangle shape. Now cover it again with plastic sheet and refrigerate for half an hour. This will make the dough firm and will be easy to cut.
• After half an hour remove it from the fridge and cut them into slices of 1/4" thickness.
• Place the sliced cookies on a baking tray and bake for 10 - 12 mins. Check after ten mins to note if the vanilla part has turned into light golden color.
• If done, remove the cookie sheet from the oven. Let the cookies cool down for two to three minutes before taking them off the cookie sheet.