Prepare the cookie dough.
1-In a large bowl, cream together the: In a large bowl, cream together the butter and powdered sugar for about 3-5 minutes until creamy. Add egg yolks, salt and vanilla extract or choose any flavor extract you prefer (almond, peppermint, rum) and mix until well combined.
2-Divide the butter mixture into two equal: Divide the butter mixture into two equal parts.
3-For the white dough, incorporate flour using: For the white dough, incorporate flour using a spatula or wooden spoon.
4-For the chocolate dough, incorporate flour and: For the chocolate dough, incorporate flour and cocoa powder using a spatula or wooden spoon.

How to shape the cookies.
5-Take about ¼ teaspoons of white dough: Take about ¼ teaspoons of white dough and roll them into small balls.
6-Repeat with the chocolate dough: Repeat with the chocolate dough.
7-Take three balls of each color, alternate: Take three balls of each color, alternate the colors, and arrange them to form a flower shape.
8-Press them slightly to close the gap: Press them slightly to close the gap in the middle.
9-Gently roll the flower shape between your: Gently roll the flower shape between your palms until the colors begin to swirl together. Be careful not to apply too much pressure during the rolling process.
10-Once you get the desired swirl effect: Once you get the desired swirl effect press slightly to flatten.
11-Transfer the cookies onto a parchment paper-lined: Transfer the cookies onto a parchment paper-lined baking sheet.
12-Refrigerate for 15-30 minutes before baking: Refrigerate for 15-30 minutes before baking.

How to bake the cookies.
13-Meanwhile, preheat the oven to 325F (160C): Meanwhile, preheat the oven to 325F (160C).
14-Bake the cookies for 13-15 minutes until: Bake the cookies for 13-15 minutes until golden at the edges.
15-Let them cool slightly and transfer them: Let them cool slightly and transfer them to a cooling rack to cool completely.