In a medium bowl, whisk together the flour, cocoa powder, baking powder, baking soda, and salt.

In a large bowl, beat the butter, granulated sugar, and brown sugar until light and fluffy.

Mix in the egg, vanilla extract, and red food coloring until well combined.

Gradually add the dry ingredients, alternating with buttermilk, until a soft dough forms.

Divide the dough in half, wrap in plastic wrap, and refrigerate for 1–2 hours.

Preheat your oven to 350°F (175°C) and line baking sheets with parchment paper.

Roll out the dough on a floured surface to about 1/4-inch thickness. Cut out tree shapes using a cookie cutter and place them on the prepared baking sheets.

Bake for 10–12 minutes, or until the edges are set.

Let the cookies cool on the baking sheets for 5 minutes, then transfer to a wire rack to cool completely.

In a mixing bowl, combine powdered sugar, meringue powder, and water. Beat until the icing is smooth and holds stiff peaks. Adjust the consistency with more water if needed.

Divide and color the icing as desired.

Use a piping bag with a small tip to decorate the cookies with white icing as garlands and green icing for holly leaves. Add red icing dots for berries.

Sprinkle edible glitter or shimmer dust for a magical holiday sparkle. Let the icing set completely before serving.