In a large mixing bowl, whisk together the flour, baking powder, and salt. Set aside.

In a separate large mixing bowl using an electric mixer, mix the shortening and sugar together for 1 to 2 minutes or until well combined. Add the egg, milk, and vanilla extract and mix until fully combined, making sure to stop and scrape down the sides of the bowl as needed.

Add the dry ingredients and mix until fully combined. The mixture will be a little crumbly at first, but it will come together as you continue mixing it. Once the dough comes together, use your hands to form it into a ball.

Divide the dough in half. Lightly flour a piece of parchment paper, add half of the dough, top with another piece of parchment paper, and roll the dough to ¼-inch thick between both pieces of parchment paper. Repeat with the other half of the dough between two separate pieces of parchment paper. (This dough doesn't require any dough chilling, but if you prefer colder dough so that it's easier to work with you can place both pieces of rolled out dough between the parchment paper on a baking sheet and refrigerate for 30 minutes to one hour.)

Bake for 11 to 13 minutes or until the tops of the cookies are set and the bottom edges are lightly browned.

Remove from the oven and allow to cool on the baking sheets for 10 to 15 minutes, then transfer the cookies to a wire rack to cool completely.

Mix in 1 additional teaspoon of milk at a time until the icing has thinned out and reached a medium consistency. You want it to be thick enough to outline the cookies, but thin enough to still be able to fill them. To test the icing, lift your whisk or spoon from the mixing bowl; the ribbons of icing should take about 4 to 5 seconds to melt back into the bowl of icing. If it’s too thick, add more milk to thin out the icing. If it’s too thin, add more powdered sugar to make the icing thicker.

Remove a little bit of the icing, place it into a small bowl, and mix in the black gel food coloring (this will be for the eyes and mouth). Divide the remaining icing between two separate bowls. Add a little red gel food coloring to one to create a pink icing and yellow gel food coloring to the other one to create a yellow icing. Cover the bowls with damp paper towels or place the colored icings into separate piping bags until you’re ready to use them.

Outline a cookie with the icing, then fill the cookie with a thin layer of icing. Use a toothpick or scribe to move the icing around and fill in any empty spots. If needed, gently tap or shake the cookie to help the icing settle in a smooth layer.

Gently press the top of the iced sugar cookie into the same color of sanding sugar. Make sure not to press too hard or the icing will start to come over the edge of the cookie. You can also sprinkle the sanding sugar on top and shake off any excess. Repeat with the remaining sugar cookies until they’re all iced and covered in sanding sugar.

Using the black icing, add a small dot to the chick cookies for the eyes and three small dots to the bunny cookies for eyes and a mouth.

Allow the icing to harden completely. This can take up to one day, so I prefer to make my cookies the day before and store them in a container to let the icing harden overnight. You can also let them sit on the counter at room temperature overnight (the icing will keep them from drying out).