In a large mixing bowl, beat together the confectioner's sugar and butter for about 2 minutes, until fluffy.

Mix in the vanilla, flour, and cornstarch until well combined.

Cover the bowl with plastic wrap and put dough in refrigerator for 30 minutes. Set a timer so you don't forget. (In the notes I'll tell you what to do if you do forget).

Once 30 minutes is up, preheat oven to 350° F. Cover baking sheets with parchment paper.

Scoop batter with a 1" cookie dough scoop and place on baking sheet leaving room for the cookies to spread a bit.

Bake for 10-12 minutes, the edges should just start to brown.

Allow cookies to cool on cookie sheet for 2 minutes, them move them to cooling rack.

Once all cookies are baked and cooled a bit make the glaze.

In a medium bowl mix together the confectioner's sugar, butter, and vanilla.

Add in the milk a little at a time, mixing between each add so as to reach the desired consistency.

Place the cooling racks on the baking sheets covered with parchment paper to limit the mess of glazing the cookies.

Have any sprinkles handy. The glaze sets fast. I suggest glazing a few cookies then adding sprinkles and repeating over and over again until they are all done.

Use a spoon to drop the glaze onto the cookies, making sure it covers most of the top.

When all the cookies are glazed and sprinkled, allow them to set for at least 15 minutes before storing in an air tight container.