These are the sweetest little cookies rolled in colorful sprinkles with matching powdered sugar frosting.
Preheat oven to 350 degrees F., and prepare sheet pans with parchment.
In a large bowl mix the butter, shortening, sugar, egg yolk, and vanilla until completely mixed.
Mix in the flour and salt until combined and the dough holds its shape.
Place the nonpareils in a bowl big enough to roll the dough balls.
Shape the dough into 1" balls then immediately roll in the nonpareils. The warmth of your hands helps make the dough balls a little soft so the nonpareils will stick better.
Place the balls 1" apart on the baking sheets then press your thumb into the center of each dough ball.
Bake for about 10 minutes until lightly browned. Then remove from oven to cooling rack.
Mix the sifted powdered sugar and milk to make a smooth mixture. This icing sets up hard after it sits for a couple of hours.
Separate the icing into three small bowls. Tint one pink and one red with the food coloring.
With a small spoon fill each cookie with one of the icings. You can put the icing in a piping bag and pipe into the cookies.