One of the most popular Dutch sweet treats is a spice-filled, crunchy cookie called speculaas, or "mirror," since the cookies reflect the image of the molds from which they're shaped.
In a medium bowl, whisk together flour, baking soda, salt, and spices.
In the bowl of a stand mixer fitted with the paddle attachment, beat together butter and sugars on medium speed until light and fluffy, 2 minutes. Reduce speed to low; beat in half the flour mixture. Beat in milk, followed by remaining flour mixture. Shape dough into a flat disk, wrap in plastic, and refrigerate until firm, at least 2 hours or up to overnight.
Line three baking sheets with parchment. Dab speculaas mold all over with a small piece of dough (this provides a light buttery coating that prevents sticking). Generously sprinkle mold with flour, tapping to remove excess. Take a piece of dough that is roughly the same size as the mold; using your palm, press into mold. Using a long, thin knife, scrape off excess dough. Invert mold over a prepared baking sheet; rap far end of the mold against the sheet, holding it at an angle to release the formed cookie. Sprinkle mold with more flour; repeat with remaining dough. Gather scraps (refrigerate if dough gets too soft) and form more cookies. Freeze at least 30 minutes.
Preheat oven to 350 degrees. Bake until firm and golden, 15 to 20 minutes. Transfer parchment with cookies to wire racks; let cool completely.