Line 2 sheet pans with parchment paper. Set aside.

Place very soft butter in a medium-size mixing bowl. Stir with a wooden spoon or sturdy spatula until nice and smooth. Add sugar and vanilla. Mix together by hand for about 30 seconds, until fluffy and well blended.

Add the flour, cornstarch and salt. Stir until flour is completely incorporated. The dough will look a little shaggy. Turn out onto a lightly floured surface and press dough in a ball. Knead a few times until fairly smooth then form into a ball again and press with your hands into a flat disk.

On a lightly floured work surface, roll out dough to a ⅜-inch thickness. Keep work surface, dough and rolling pin lightly dusted with flour. Cut desired shapes and place on prepared pans. Re-roll scraps as many times as needed to use up the dough.

Place cutouts in the refrigerator for at least one hour or up to 24 hours.

When ready to bake, preheat oven to 375˚F. Remove cookies from refrigerator and bake for 12-14 minutes or until just beginning to turn golden at the edges. Rotate pans halfway through for even browning. Cool completely before icing.

To glaze the cookies, hold onto the edges of a cookie and dip the top surface into the glaze, being sure the entire surface of the cookie touches the glaze. Pull cookie up and out of the glaze. Allow excess glaze to drip back into the bowl. When glaze stops dripping, quickly flip the cookie right side up and give it a gentle jiggle to allow the glaze to flow evenly over the surface then sprinkle with jimmies, nonpareils, sprinkles, etc. Repeat with remaining cookies. Allow glaze to dry for at least 30 minutes.