Christmas Pinwheel Cookies

In a small bowl, whisk together the flour, baking powder, and salt. In the bowl of a stand mixer fit with a paddle attachment and set on medium speed, beat the butter and sugar until light and fluffy, about 3 minutes. Add the egg and vanilla and beat to incorporate. Reduce the mixer's speed to low and blend in the flour mixture one-third at a time.

Turn the dough out onto a lightly floured surface and knead a few times. Roll it into a ball and flatten into a disk. Halve the dough. Tint one portion with green food coloring and the other with red. Shape each portion into a rectangle, then wrap it in plastic and refrigerate 1 hour.

Roll out each portion of dough on a sheet of parchment paper into a 10- by 13-inch rectangle. Stack them on a baking sheet, cover the sheet in plastic and refrigerate once more for 30 minutes.

Peel the paper from one portion of dough, then center and layer it onto the other. Press gently to adhere the pieces and trim the edges so that they are straight and evenly layered. Starting from a long edge, roll the dough tightly into a tube. Cover with plastic and refrigerate 2 hours.

Heat the oven to 350°. Line two baking sheets with parchment paper. Trim the uneven end from the dough tube, then cut it crosswise into ¼-inch slices. Arrange the cookies on a baking sheet, spacing them 2 inches apart.

Bake the cookies until set and lightly golden on the bottom, about 10 minutes. Let the cookies cool 5 minutes on the baking sheets, then transfer to a rack to cool completely.