In a large bowl combine the flour, baking powder and salt. Whisk together.
In the bowl of a mixer combine the butter and sugar. Cream together on medium/high until the mixture is light and fluffy.
Beat in the eggs one at a time. Make sure to fully mix in each egg before adding the next. Then add the vanilla and mix.
Turn the mixer to low and slowly add the flour mixture. Mix until everything is incorporated.
Cover the bowl and chill in the refrigerator for an hour or more.
Preheat the oven to 350 degrees Fahrenheit. Line baking sheets with parchment paper.
When the dough has fully chilled, scoop out 1/4 cup portions and roll into a ball. Then place the balls on the parchment lined baking sheets about 2-3 inches apart. Then flatten the balls slightly to form disks. Repeat with the remaining dough.
Bake the cookies for 10-12 minutes or until they are just set. DO NOT OVERBAKE! The edges should be just be lightly turning brown. You do not want the cookies to get any color. If so they will start to harden.
When the cookies are just set, remove them from the oven and let cool on the baking sheets for 5-10 minutes. Then transfer them to a wire rack to fully cool.
While the cookies are cooling place the confectioners' sugar to a mixing bowl. Add the melted butter, vanilla and milk. Whisk the mixture until smooth. If the frosting is too hard, slowly add another tsp of milk to the mixture. Whisk and repeat until you have the desired texture. If you want colored frosting add the desired color to the frosting now and whisk.
Frost the cookies and add sprinkles to finish the cookies.