1 cup butter (room temperature)
1 cup sugar
2 egg yolks
2 teaspoons vanilla
1/4 cup + 2 tablespoons milk
3 cups flour
1 teaspoon baking powder
1/4 teaspoon salt
2 ounces dark chocolate, to be melted
Make the dough and let chill for several hours
Beat the room temperature butter, sugar and egg yolks together until light and fluffy. Add the vanilla and slowly mix in the milk. In a separate bowl, mix together the flour, baking powder until blended. Slowly add the dry ingredients to the creamed butter and sugar, scraping down the sides of the bowl occasionally to ensure even mixing. Once the dough is mixed, divide into half and return one half to the mixer. Break the chocolate into small chunks and place in a microwave-safe glass container. Heat the chocolate in short 10 - 15 second bursts, stirring and letting rest a minute between heating cycles. Once the chocolate is melted, add it to the dough in the mixer and blend, using a spatula to get all the chocolate incorporated. Wrap both halves of the dough in plastic wrap and let chill for several hours or overnight, whatever is more convenient.
Roll the dough into layers
Remove the dough from the refrigerator and place on lightly floured wax paper. Use a different sheet of wax paper for each half. Shape the dough into a rough rectangular shape. Using a rolling pin dusted with flour, roll each dough ball into a 9 x 13 inch rectangle, dusting with more flour as needed to prevent sticking. You can slice off any rounded edges and tack them on other parts of the dough and continue rolling to get a nice rectangle of consistent thickness. Getting a rectangle (or at least straight edges) goes a long way towards having all the cookies look nice. Try to get each dough half's rectangle the same dimensions as any longer portions you will have to cut off and use for "tasting" cookies. Carefully lift one rolled half using the waxpaper and invert it over the other half. Gently peel off the top wax paper. Slice off any excess dough to make nice edges and then tightly roll the 2 layers, starting from the narrower end. It is most important to get the roll started without any air gaps in the center. By now the dough will have warmed up and be soft, so wrap it in plastic wrap and place in the refrigerator for several hours or overnight. If you have a round bottomed, cylindrical container to set the roll in, so much the better, as the dough will want to flatten out.
Slice the roll and bake the cookies in 375°F oven for 8 - 11 minutes
Preheat oven to 375°F. Remove the rolled dough from the refrigerator and unwrap on a cutting board. If the dough is a little out of round, you can work it a little to remove the flat spot. Applying pressure along the length of the roll as you gently roll it will also help minimize any air pockets or gaps while elongating the dough. Don't overwork the dough since this will warm it up. Use a knife to slice the dough into 3/8 inch thick slices.If the dough is a little soft, you can leave all the slices intact on the roll, and gently roll the entire roll to get them nice and round. Carefully place the slices on ungreased cookies sheets about 1 inch apart. Slice up all the dough at once since it is difficult to slice (and keep round) and handle once it gets to room temperature. If you don't have enough cookie sheets to do this, just return the roll to the refrigerator to keep it firm. Bake for 8-11 minutes or until the cookies begin to brown. These cookies are fairly forgiving to under/overcooking, so if you like your cookies crisp/crunchy, go for more browning. Barely browned cookies will be not be crisp but will have a delicate crunch. Remove cookies from baking sheet and let cool on cooling racks.