Preheat Oven: Preheat the oven to 350°F (177°C). Line two baking sheets with parchment paper and set aside.

Cream Butter and Sugar: In a large mixing bowl, use a hand mixer or stand mixer fitted with the paddle attachment to cream together the butter and granulated sugar on medium speed for 2-3 minutes, or until light and fluffy. Start Timer

Add Wet Ingredients: Beat in the egg, egg yolk, milk, and vanilla extract, mixing until combined and smooth. Scrape down the sides of the bowl as needed.

Add Dry Ingredients: In a separate bowl, whisk together the flour, baking powder, salt, and baking soda. Gradually add the dry ingredients to the wet ingredients, mixing on low speed until a soft dough forms.

Add Sprinkles: Fold in the red and green jimmies sprinkles until evenly distributed throughout the dough.

Scoop and Roll: Scoop about 2 tablespoons of dough per cookie and roll into balls. Roll each ball in granulated sugar before placing it on the prepared baking sheets, spacing cookies about 2 inches apart. (Optional to chill: you can chill the cookie dough prior to baking if desired. From 1 hour or up to 3 days covered in the fridge.. Allow to come to room temperature, then roll and bake as directed below.)

Bake: Bake for 8-10 minutes, or until the edges are set and just barely golden. The centers should look slightly soft. Do not overbake. Start Timer

Cool: Allow cookies to cool on the baking sheet for 3-5 minutes, then transfer to a wire rack to cool completely. Start Timer

Enjoy: Sprinkle any remaining granulated sugar on top and garnish with more sprinkles for a festive look!