1. Make the Cookie Dough

• In a large bowl, beat the softened butter and granulated sugar together for 2-3 minutes until light and fluffy.
• Add the egg and vanilla extract, mixing until smooth and fully incorporated.
• In a separate bowl, whisk together the flour, cornstarch, baking powder, and salt.
• Gradually mix the dry ingredients into the butter mixture until a smooth dough forms. Avoid overmixing.

2. Roll and Coat in Sprinkles

• Preheat the oven to 350°F (175°C) and line two baking sheets with parchment paper.
• Scoop 1 tablespoon of dough and roll it into a smooth ball.
• Roll each ball in Christmas-colored sprinkles, pressing gently to coat evenly.
• Place the sprinkle-coated balls on the prepared baking sheets, spacing them about 2 inches apart.

3. Bake the Cookies

• Bake for 10-12 minutes, until the edges look set but the centers remain soft.
• Let the cookies cool on the baking sheet for 5 minutes before transferring to a wire rack to cool completely.

4. Make the Buttercream Frosting (Optional)

• In a bowl, beat the softened butter until creamy.
• Gradually mix in the powdered sugar, stirring until smooth.
• Add the vanilla extract and salt, then add milk, one tablespoon at a time, until the frosting reaches your desired consistency.
• Divide the frosting into two bowls. Use red gel coloring for one bowl and green gel coloring for the other.

5. Assemble the Layered Cookies

• Spread or pipe a small amount of frosting onto the bottom of one cookie. Place another cookie on top, pressing gently to sandwich them together.
• Optionally, decorate the tops of the cookies with piped frosting and more sprinkles.