In a mixing bowl, cream together the softened butter and granulated sugar until light and fluffy. This process typically takes around 2-3 minutes. Using an electric mixer or stand mixer will make the task easier, but hand mixing works just as well.

Next, add the egg and pure vanilla extract to the creamed butter and sugar mixture. Beat until well combined and smooth.

In a separate bowl, whisk together the all-purpose flour, salt, and baking powder. Gradually add this mixture to the wet ingredients, mixing until the dough forms. Be careful not to overmix, as this can lead to tough cookies.

Divide the dough into two equal parts. Place one portion back in the mixing bowl. Add a few drops of red food coloring and mix until the dough turns a vibrant shade of red. Repeat the process with the second portion of dough, using green food coloring instead.

Take a piece of plastic wrap and place it on a clean surface. Roll out the red dough into a rectangular shape, about ¼ inch thick. Repeat the process with the green dough, ensuring that it matches the dimensions of the red dough.

Carefully lift the green dough and place it on top of the red dough. Gently press the two layers together to create a firm bond. Starting from one end, tightly roll the dough into a log shape. Wrap the log with plastic wrap and refrigerate for at least 2 hours or until firm.

Preheat your oven to 350°F (175°C). Line a baking sheet with parchment paper. Remove the dough log from the refrigerator and unwrap it. Using a sharp knife, slice the log into ¼ inch thick cookies. Place the cookies on the prepared baking sheet, leaving some space between each.

Bake the cookies for 10-12 minutes or until the edges turn golden brown. Allow them to cool on the baking sheet for a few minutes before transferring to a wire rack to cool completely.