Cream the Butter: In the bowl of a stand mixer fitted with a paddle attachment, add 1 cup of softened butter. Mix on medium speed until creamy and light in color, about 2 to 3 minutes.

Incorporate Powdered Sugar: Gradually add 2 cups of powdered sugar, continuing to mix on medium speed until fluffy and pale, roughly 3 to 5 minutes.

Add the Egg: Crack 1 large egg into the mixing bowl and blend until completely incorporated, about 1 to 2 minutes.

Mix Dry Ingredients: In a separate bowl, sift together 3 cups of flour, ½ cup of black cocoa powder, ½ cup of Dutch process cocoa powder, and ½ teaspoon of salt. Gradually add to wet ingredients, mixing on low until just combined.

Form the Dough: Turn the dough out onto a clean surface and bring it together into a cohesive ball, kneading gently for about a minute.

Chill the Dough: Wrap the formed disc of dough in plastic wrap and chill in the refrigerator for at least 30-45 minutes.

Roll Out the Dough: Once chilled, roll it out between two sheets of parchment paper until it reaches a thickness of 4 mm.

Cut the Cookies: Cut out shapes from the rolled dough using cookie cutters and place on a lined baking tray.

Preheat and Bake: Preheat your oven to 160°C (320°F). Bake cookies for about 10 minutes until set but not over-browned.

Cool the Cookies: Allow cookies to cool for 5 minutes on the baking sheets before transferring to a cooling rack.

Prepare Royal Icing: Beat an egg white until frothy, gradually add powdered sugar, beating until shiny peaks form.

Color & Decorate: Divide royal icing among bowls, mix in gel food coloring, and decorate cookies.

Let Icing Set: Allow decorated cookies to dry for 3 to 6 hours at room temperature.