In a large mixing bowl, add the flour, powdered sugar, cocoa powder, and salt. Whisk together until fully combined.
Add the cold, cubed butter and use a pastry cutter or your fingertips to work the butter into the flour mixture until it resembles bread crumbs.
Add the vanilla extract and 2 tablespoons of cold water. Use a knife to cut the liquid into the dough. It will take a while for the dough to come together. If it looks dry add 1 tablespoon of cold water and keep cutting the dough. You may need to add the final tablespoon to bring the dough together (see notes).
Lightly flour a work surface and turn the dough out onto it. Use your hands to bring the dough together into a smooth ball of dough. Put the dough back into the mixing bowl and refrigerate for 20 minutes.
Prepare two cookie sheets with parchment paper. After 20 minutes, remove the dough from the refrigerator and divide it into 20 equal portions of dough. Roll each portion into a ball.
Brush your cookie stamp with cocoa powder and press it onto the small ball of dough. As you press, rotate the cookie stamp in a circular motion. This will help the dough to spread out to the edges of the stamp.
Lift the cookie stamp away from the dough revealing the embossed pattern. Use a palette knife to lift the cookie from your work surface and onto the cookie sheet. Repeat for the remaining dough balls.
Put the cookie sheets in to the refrigerator to chill for 2 hours. This step is crucial.
Preheat the oven to 350 degrees F.
Once the shortbread chills for two hours it will feel hard to the touch. Place the cookie sheets into the oven and bake for 11 minutes.
Remove the shortbread from the oven and allow the cookies to cool on the cookie sheet before serving.
Notes
Storage and Make-ahead: The dough can be kept in an airtight container in the fridge for two days. Once baked, store the cookies in an airtight container at room temperature for up to two weeks.
Chocolate Shortbread can be frozen for up to one month.
If you are not using a cookie stamp, the dough can be rolled out after the first 20 minutes of chilling and cut with regular cookie cutters. However, you must still chill the cut-out dough for at least one hour before baking.
The chocolate flavoring comes from the cocoa powder. We recommend a Dutch-processed cocoa powder for its smoother taste and dark coloring.
Be sure to spoon and level your flour. If you scoop the measuring cup into flour, you risk compacting it. If this recipe has too much flour, the resulting shortbread will be too dense and too crumbly. If you want to weigh your flour, it should weigh 250 grams.
When making shortbread, it’s important to use high-quality, very cold butter. Measure the butter properly because adding too much risks the dough spreading in the oven. If you want to weigh it out, it should be 227 grams.
Using a pastry cutter to work the butter into the dough is great because it means you won’t transfer heat from your hands. If you don’t have a pastry cutter, use only your fingertips and avoid rubbing the mixture with your palms. Keeping shortbread dough as cold as possible will yield better results.
When it’s time to add the water and bring the flour together into a dough, add the water gradually so you can judge how much you will need. You might not need all four tablespoons. This will depend on the brand of flour you choose, how it reacts to absorbing flour, and how it is measured. It will take several minutes to cut the liquid into the dry flour mixture, so be patient. It will come together!
When you bring the dough together into a ball with your hands, we recommend running your hands under a cold tap first. Try to handle the dough as little as possible. You shouldn’t have to knead it but merely shape it into a smooth-looking ball.
Chilling the dough briefly before portioning it will make it easier to handle and help when embossing the shortbread.
The second chill once the shortbread has been stamped is very important. Do not skip this step, or your shortbread will spread in the oven and lose its pattern.
Toward the end of baking, the shortbread will puff up a bit, but as the shortbread cools, it should settle back down, and your pattern will look beautiful again!
You might consider adding a glaze to the shortbread for a different look. We also have dry-brushed the stamped Chocolate Shortbread with edible glitter, which looks really pretty.