Jam-Buttercream Frosting:
1.    Using a stand mixer with the paddle attachment on medium-high speed, cream the butter until light and fluffy, a few minutes. Add the powdered milk to the sugar. Decrease the mixer speed to medium-low. Gradually mix in the sifted powdered sugar until fully incorporated.
2.    Slowly add the preserves. Increase the speed to medium-high and whip for 3 or 4 minutes. Spread frosting on cookies, decorate with sugar pearls and sparkling sugars and serve.