Cream the Butter and Sugar: In a large bowl, beat together the softened butter and granulated sugar until the mixture is light and fluffy., Add Eggs and Vanilla: Mix in the eggs one at a time, followed by the vanilla extract, blending until combined., Combine Dry Ingredients: In a separate bowl, whisk together the all-purpose flour, baking powder, and salt. Gradually add this dry mix to the wet ingredients, stirring until just combined. Avoid over-mixing., Chill the Dough: Wrap the dough in plastic wrap and chill it in the refrigerator for at least 30 minutes. This step helps to firm up the dough, making it easier to roll out., Roll Out the Dough: On a lightly floured surface, roll out the chilled dough to about ¼ inch thick. Use cookie cutters to cut into desired shapes, placing them on a baking sheet lined with parchment paper., Preheat the Oven: Preheat your oven to 350°F (175°C)., Bake Cookies: Bake in the preheated oven for 8-10 minutes or until the edges are just beginning to turn golden. Remove from the oven and let them cool on the baking sheet for a few minutes before transferring to a wire rack to cool completely., Prepare the Frosting: In a small bowl, mix powdered sugar with a little milk and vanilla to create a frosting that can hold its shape. Adjust the consistency by adding more sugar or milk as needed., Frost and Decorate: Use piping bags to decorate the cookies with frosting. Add sprinkles or any additional decorations while the frosting is still wet for the best adherence., Cool Completely: Allow the cookies to cool completely before stacking them or placing them in containers. This prevents them from sticking together., Store: Keep cookies in an airtight container at room temperature for up to one week.