Festive Marbled Sugar Cookies

Ingredients:

Cookie

• 2 and 3/4 cups premium flour
• 0.5 tsp baking powder
• 1/4 teaspoon fine salt
• 220 g unsalted butter, room temperature
• 3/4 cup granulated sugar
• 1 tsp vanilla extract
• 1 large egg
• Powdered sugar, for dusting
• Special equipment: round cookie cutter with a diameter of 5 cm.

Royal icing

• 450 g of powdered sugar
• 2 tbsp. dry egg white
• Red and green gel food coloring
• Edible glitter or decorative sprinkles

Preparation:

1. Cookie:
   
   In a medium bowl, combine the flour, baking powder, and salt. In a large bowl, beat the butter and sugar with a mixer on medium speed until light and fluffy, about 4 minutes. Increase the mixer speed to medium-high, add the vanilla extract and egg, and beat until fully incorporated. Reduce the mixer speed to low, add the flour mixture in 2 additions, and knead until smooth. Form the dough into a disk. Wrap and refrigerate to set, about 1 hour.
2. Line 2 baking sheets with parchment paper.
3. Generously dust a work surface with powdered sugar. Roll the dough out to a 1 cm thickness, dusting with additional powdered sugar as needed. Return the dough to the refrigerator if it becomes too soft. Using a 5 cm cookie cutter, cut out circles from the dough and place them 5 cm apart on the prepared baking sheets. Gather up the dough scraps and cut out more cookies. Refrigerate the baking sheets until the dough hardens, about 1 hour.
4. Position racks in the upper and lower thirds of the oven and preheat to 350°F (175°C). Bake the cookies, rotating the baking sheets halfway through, until golden brown around the edges, 9 to 11 minutes. Let cool completely on the baking sheets.
5. Royal icing:
   
   Combine the powdered sugar and dry egg whites in a large bowl. Add 7 tablespoons of water and beat with a mixer on medium speed until soft, glossy peaks form, adding an additional 1 tablespoon of water if necessary to create a smooth glaze that thickly coats the back of a spoon.
6. Line a baking sheet with parchment paper and place a wire rack on top.
7. Place 1/4 cup of frosting in 2 small bowls. Add 9 drops of red food coloring to one bowl and stir. Add 2 drops of green food coloring to the second bowl and stir. Transfer the remaining white frosting to a clean rimmed baking sheet and spread or shake to coat evenly. Drizzle red frosting over the white frosting, then drizzle green frosting over the white frosting.
8. Place the cookies, one at a time, frosted-side up on a baking sheet. Remove them one at a time, gently shaking them to remove excess frosting, and place them frosted-side up on the prepared wire rack. Sprinkle with edible glitter or sprinkles, if desired. Let the frosting set completely before serving, about 1 hour.