Set the oven to 350°F (175°C) and prep baking sheets with parchment or mats. Combine flour, leaveners, and salt, then set the bowl aside.
Mix butter and sugar until light and airy, about 3–5 mins. Once fluffy, stir in the milk and vanilla.
Add the dry ingredients to the wet mix a little at a time, stirring softly after each batch. Once it’s all combined, you’ll have a thick dough.
Scoop roughly ¼ cup of dough onto the prepared baking sheets, ensuring a 3-inch gap between each scoop.
Lightly press down each scoop with your hands, but no need to stress about making them perfectly even!
Bake for 13–16 minutes, check doneness with a toothpick. Cool briefly, then move to rack.
While your cookies cool, it’s time to make the icing. Whisk sugar, water, and vanilla until smooth.
Add more hot water if too thick. Once the cookies are completely cool, spread a thin layer of the white icing over the flat side of each cookie. Set the icing aside for 15 minutes.
Melt dark chocolate and blend into the white icing. If too thick, add more hot water. Spread the chocolate icing over the other half of each cookie, making sure it’s evenly covered.
Rest cookies 15 minutes for the icing to harden. Then, they’re ready to be enjoyed!