In a large mixing bowl, combine the all-purpose flour, baking powder, and kosher salt. Set aside. In another bowl, cream together the unsalted butter and granulated sugar using an electric mixer until light and fluffy.
Add the eggs one at a time, mixing well after each addition. Stir in the pure vanilla extract until fully incorporated.
Gradually add the flour mixture to the wet ingredients, mixing until a dough forms. Divide the dough in half.
To one half of the dough, add the unsweetened cocoa powder. Mix until the cocoa is fully combined, creating a chocolate dough.
On a lightly floured surface, roll out the vanilla dough into a rectangle about ¼ inch thick. Repeat with the chocolate dough, ensuring both rectangles are of similar size.
Place the chocolate dough on top of the vanilla dough. Gently roll the dough into a tight log, starting from one of the long edges. Wrap the log in plastic wrap and refrigerate for at least 1 hour.
Preheat your oven to 350°F (175°C). Unwrap the dough log and slice it into ¼-inch thick rounds. Place the slices on a baking sheet lined with parchment paper, leaving space between each cookie. Bake for 10-12 minutes, or until the edges are lightly golden.
Allow the cookies to cool on the baking sheet for a few minutes before transferring them to a wire rack to cool completely. Enjoy your Chocolate Vanilla Pinwheel Cookies with a glass of milk or your favorite beverage!