In a glass measuring cup, pour ¾ cup of boiling water into it. Add in the gelatin powder and stir until the gelatin is dissolved. Let sit until cooled to room temperature, but still liquid consistency.
Add half of the powdered confectioners sugar into the bowl for the electric mixer. When the gelatin mixture is room temperature, add ½ tsp of the vinegar into the powdered sugar and turn the mixer on low. Slowly pour the gelatin mixture into the bowl as it is mixing. ONLY pour in ¼ cup of the gelatin mixture at first. Then turn the mixer off and add the rest of the powdered confectioners sugar in. Add in another ¼ of the vinegar and turn the mixer back onto low, slowly pouring in another ¼ cup of the gelatin mixture in while mixing. Add in another ¼ tsp of vinegar in while mixing, then add in the rest of the gelatin mix. Let combine completely.
Turn the mixer up to medium high and every minute add in the rest of the vinegar ¼ tsp at a time until you’ve added a total of 1½ tsps into the icing. Keep the mixer going on medium high while you do this. Then place the mixer on high and beat the icing for 2 minutes.
Add any color of food coloring you desire and fold into the icing gently until the color is evenly distributed. Using either a piping bag or a ziplock bag, add your icing inside. Seal off the tops with a rubber band, icing band, or a clip so the icing doesn’t slip out the top. Snip the corner or bottom of the bag, realize that the higher up you snip the larger the hole will be. If I am icing cookies, I like the hole to be really small, but if we are trying to make gingerbread houses I like the hole to be on the larger size.
Ice the baked good, the icing will set relatively quickly so be mindful of that. When I iced the sugar cookies, it only took the icing 5 minutes for the top layer to being to set. For the icing to fully set, it took about 45 minutes. Store leftovers in an airtight container for up to 2 days. Whatever air is in the container will cause the icing to harden, so place plastic wrap right up against the top of the icing to keep it’s consistency.