Line 2 sheet pans with parchment paper. Set aside.

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

Add the flour and cornstarch. Stir until dry ingredients are incorporated. The dough will be a little shaggy. Turn the dough out onto a lightly floured work surface and gather into a ball.

Knead 5-6 times until fairly smooth and all the small pieces are worked in. Form into a ball again and flatten with your hand to form a flat disk. Turn the disk to coat both sides with flour.

Roll out the dough to an approximate ⅜-inch thickness (see Café Tips above in the post). Keep work surface, dough and rolling pin lightly dusted with flour. Cut out Christmas trees (in one or more sizes) and transfer to prepared pans with a thin, metal spatula. 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 350˚F. Remove 1 pan of cutouts from the refrigerator and bake for 12-14 minutes, or until just beginning to turn golden at the edges. Rotate pans halfway through for even browning. Repeat with the second pan of cutouts.

Cool completely before icing.

Transfer the glaze to a small shallow bowl (a little bigger than your cookies). With a toothpick, swirl a small amount of two green gel food colorings through the icing in the bowl. Don’t swirl too much or the icing will become a solid color. Use a light hand with the gel food coloring. A little goes a long way!

To glaze the cookies, hold onto the edge of a cookie and dip the top surface into the glaze, being sure all of the surface touches the glaze. Pull cookie straight up and out of the glaze. Allow excess glaze to drip into another bowl or plate (this will keep the glaze from getting murky) for about 30 seconds. When glaze stops dripping, quickly flip the cookie to the right side up and give it a gentle jiggle to allow the glaze to flow evenly over the surface. Repeat with remaining cookies.

Place cookies on a cooling rack and allow glaze to dry completely.