Tasty Thursdays....French Swirl Butter Cookies

I remember going to the cookie section of the bakery with my mom and drooling over the chocolate swirled butter cookies when we were kids.  My love for butter cookies only flourished when we were in Paris,with all the delicious butter cookies and pastries, I was in heaven!  So naturally, I couldn't wait to make these swirl butter cookies when I found this recipe.  Yields 20 cookies.

Ingredients per layer (note you'll need 2 layers):
1/2 egg yolk
5 tbsp butter
8 tsp sugar
1/8 tsp salt
1/2 tsp vanilla extract
3/4 cups flour
**For the chocolate layer reduce the flour to 1/2 cup, and add a 1/4 cup of cocoa powder

Directions:
- Bring a pot of water with egg to a boil, remove from heat and cover for 10 minutes.  Transfer the egg into a bowl of ice water.  Remove the shell and slice in half.  Remove half of the egg yolk and press through a sieve.
- In a mixer, blend the sugar, salt, butter, and egg yolk till smooth.
- Add the vanilla extract, and flour and mix till combined about 1 minute. 
- Roll dough into a log and wrap in parchment paper, seal both ends (I stapled my ends).  
- Freeze for an hour (at this point dough can be kept frozen for up to 2 weeks)
- Roll dough out on lightly floured parchment paper, you'll want a 6 by 8 rectangle.  
- Layer the chocolate dough over the plain butter dough and roll into a tight log.  

- Freeze for an hour.
-Preheat the oven to 350 degrees, bake for 12-15 minutes
- Transfer to wire rack to cool completely