Gingerbread Cookies:

In a large mixing bowl or the bowl of a stand mixer, mix butter and brown sugar on high speed until smooth and creamy, about 30 second. Add the black treacle or molasses, followed by the egg and milk, and continue mixing on medium-high speed until well combined, about 1 minute more.

In a separate bowl, whisk flour, ginger, cinnamon, baking soda, cloves, nutmeg, and kosher salt.

Add dry ingredients to the butter and mix on medium-high speed until just barely combined, with no dry pockets remaining. Do not overmix.

Flatten dough into a large disc. Wrap in clingfilm/plastic wrap and refrigerate until firm enough to roll, at least 4 hours and up to 2 days.

Line a half-sheet rimmed baking tray with parchment or a silicone mat.

Unwrap the chilled dough and cut the disc in half. Place half of the dough on a floured surface.

Roll to approximately 1/4-inch thickness.

With a snowflake or other metal cookie cutter, cut into desired shapes.

With a flat metal spatula, transfer cookies to prepared tray.

Re-roll scraps and cut remaining dough.

Chill cut cookies in the refrigerator for 30 minutes, or freeze for 15 minutes. (If your tray doesn’t fit in the refrigerator, you can stack the cut cookies between squares of parchment and chill the stacks.)
Meanwhile, preheat oven to 350° F (176° C).

Bake, 1 tray at a time, for 10-12 minutes, or until very light brown around the edges.

Cool on tray for 5 minutes, then transfer to a wire rack to cool completely. Repeat with remaining dough.

Royal Icing:

In a large mixing bowl or the bowl of a stand mixer, whip egg white to soft peaks.

Add confectioner’s sugar, 1/2 cup at a time, and mix on high speed until meringue turns smooth and glossy, with stiff peaks. If necessary, add a bit more confectioner’s sugar to adjust the consistency. The royal icing should be thick, but pipeable.

With a flexible rubber spatula, scoop royal icing into a piping bag fitted small round tip. (I used a 1/16th-inch round tip.) Pipe as desired.

Allow decorated cookies to sit, uncovered, until icing sets. Store in an airtight container at room temperature for up to 5 days.