In the bowl of a stand mixer fitted with paddle attachment, beat butter and sugar at medium speed until fluffy, 3 to 4 minutes, stopping to scrape sides of bowl. Add egg and vanilla, beating until combined.

In a medium bowl, whisk together flour, baking powder, and salt. With mixer on low speed, gradually add flour mixture to butter mixture, beating until a dough forms. Turn out two-thirds of dough (about 598 grams) onto a clean surface, and knead dough if any flour bits remain. Shape into a disk, and wrap in plastic wrap. Refrigerate for at least 1 hour.

Add cinnamon and nutmeg to remaining dough. Beat at low speed until combined. Turn out onto a clean surface, and shape into a disk. Wrap in plastic wrap, and refrigerate for at least 1 hour.

Let doughs stand at room temperature for about 5 minutes. On a lightly floured sheet of parchment paper, roll plain dough into a 14x12-inch rectangle. Transfer dough on parchment to a baking sheet, and refrigerate for 15 minutes. Repeat procedure with spiced dough.

Transfer plain dough on parchment to a flat surface. Carefully invert spiced dough on top of plain dough. Between sheets of parchment, roll over doughs a few times to press together. Peel away top sheet of parchment. Starting with one long side, roll dough into a log, using bottom sheet of parchment to help lift and roll and rolling as tightly as possible to avoid gaps. (If dough cracks, let stand for a few minutes until pliable). Trim ½ inch off each end. Tightly wrap in parchment, twisting ends to seal. Refrigerate for at least 2 hours, or freeze until ready to use.

Preheat oven to 350°F (180°C). Line 2 baking sheets with parchment paper.

Cut log into ¼-inch-thick slices. Place 1 inch apart on prepared pans.

Bake until edges are golden brown, 8 to 10 minutes. Let cool completely on pans. Drizzle with Glaze.