Preheat your oven to 375°F (190°C) and line a baking sheet with parchment paper.

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

In a large bowl, cream together the softened butter and granulated sugar until light and fluffy. Beat in the egg and vanilla extract until well combined.

Gradually add the dry ingredients to the wet ingredients, mixing until just combined and a soft dough forms.

On a lightly floured surface, roll out the dough to about 1/4-inch thickness. Use Christmas-themed cookie cutters to cut out desired shapes.

Place the cut-out cookies on the prepared baking sheet, leaving some space between them. Bake for 8-10 minutes, or until the edges are lightly golden.

Let the cookies cool on the baking sheet for a few minutes before transferring them to a wire rack to cool completely.

While the cookies are cooling, prepare the icing. In a medium bowl, whisk together the powdered sugar, milk, and vanilla extract until smooth.

If desired, divide the icing into separate bowls and add a few drops of food coloring to each to create different colors.

Once the cookies are completely cool, decorate them with the icing using a knife, spatula, or piping bag. You can add sprinkles or other decorations while the icing is still wet.