In a large bowl using an electric mixer, or in the bowl of a stand mixer using the paddle attachment, cream butter, cream cheese, and sugar together on medium speed.

Add in the egg and vanilla extract and beat to combine.

Sift the dry ingredients (first portion of flour, baking powder, salt, baking soda) into the wet ingredients. Stir on low speed until the flour mixture is fully incorporated.

Divide dough in half. Remove half of dough from the bowl onto a sheet of plastic wrap. Add in the remaining half cup of flour. Remove the vanilla dough from the bowl. Use a rolling pin to roll dough on a piece of parchment paper, or a well-floured surface, into a 9 x 9 inch square (roughly 1/4 inch thick) and store it in the refrigerator while you make and roll the chocolate dough.

Return remaining dough to the bowl and add in the cocoa powder. Stir to combine. Roll chocolate dough into a 9 x 9 inch square, roughly 1/4 inch thick.

Remove the square of the vanilla dough from the fridge and place the square of the chocolate dough on top of the plain dough. Starting at one edge of the dough, roll the two doughs togther to form a spiral. Wrap tightly in plastic wrap and let cool in refrigerator for at least 2 hours, and up to overnight. If you will be storing for a longer period of time in the refrigerator, consider doing a double wrap.

When you are ready to bake, heat oven to 350 F. Line a cookie sheet with parchment paper or a silicone baking mat. Remove the dough log from the fridge and use a sharp knife to slice off quarter-inch thick slices. Place cookies 1-inch apart on baking sheet. Bake cookies in preheated oven for 10-15 minutes until set and just beginning to turn golden on the edges.

Let cool 5 minutes on baking sheet, then remove to wire rack to fully cool.