Cream together the butter and granulated sugar in a large bowl using an electric mixer set to medium speed.
Add the eggs, vanilla, and salt; continue blending until combined. Slowly add the flour, mixing just until combined. Be careful not to overmix!
Cover the dough with plastic wrap and chill in the refrigerator for at least an hour.
While the dough is chilling, preheat the oven to 350F and line a baking sheet with parchment paper.
Remove the dough from the refrigerator and roll it out onto a floured surface about ½-inch thick and cut into hearts (or another desired shape) with a cookie cutter. Place them onto the lined cookie sheet.
Bake in the oven for 10-12 minutes, until the cookies are set.
While baking, prepare the icing by combining the confectioners sugar, milk, and corn syrup in a small bowl. Adjust the milk measurement as needed to reach your desired consistency.
Squeeze a small amount of food coloring into the icing and use a toothpick to swirl it around for the marbled effect.
Once the cookies are done cooking and have fully cooled, dip each one into the icing face down. Lift them up and allow the excess to drip off. Add icing or edible glitter, if desired.
Place on a plate or cooling rack and allow the icing to set for about an hour. Serve with milk and enjoy!