Sift together the flour, baking powder, and salt and keep it aside.
In the mixer, beat together the butter and the sugar until light and fluffy.
Now beat in the egg and the vanilla and beat until well combined.
Add the sifted flour mixture slowly over the butter and mix until it forms a dough.
Now remove half the dough (About 9 0z) and keep it aside. This will become the vanilla layer of the cookie.
Melt the chocolate in the microwave or a double boiler slowly. Add the cocoa powder to the melted chocolate and mix well.
To the other half of the dough, add this chocolate mixture and mix again until the chocolate mixes uniformly in the dough.
Make discs of both the chocolate and vanilla dough and cover it with plastic wrap and chill for about 30 minutes. Depending on where you live, it might need more time to chill.
Roll the vanilla layer into a 12 inch square in between 2 layers of parchment or wax paper.
Also, roll out the chocolate in between 2 layers of parchment into a slightly smaller square than the vanilla.
Remove the top parchment from both the rolled out dough and slowly place the chocolate layer on top of the vanilla layer.
Slightly roll the dough again (using less pressure) to make the two layers stick to each other.
Roll the dough into a tight log. Refrigerate the dough for at least 2-3 hrs to completely harden at this stage.
Make sure you lay the dough carefully in the fridge so that the shape of the log does not get disturbed. I froze my log for about an hour and then took it out to cut.
Remove the log from the refrigerator or the freezer and roll it back and forth a couple of times to bring back the nice circle. Now using a sharp knife cut the log into ¼ inch thick cookies and place them on a parchment layered baking sheet.
Bake them at 350 F/180 C preheated oven for 9 – 12 mins.
Watch out for the base of the cookies when baking. The chocolate layer tends to become brown much quicker than the vanilla.
Cool on a wire rack and when completely cooled, store the Chocolate Pinwheel Cookies in an airtight container.