Combine the "slightly softened" butter and maraschino cherry juice in a mixing bowl. Beat on medium speed until fully mixed, allowing the cherry flavor to meld into the butter, for about 1-2 minutes.
Add the powdered sugar gradually. Start mixing on a low setting to prevent a sugary cloud, and cover the mixer with a towel. Once incorporated, increase to medium speed until it’s fluffy, about 30-45 seconds.
Incorporate cornstarch into the mixture to thicken up your frosting, gently mixing until well combined. This will ensure the perfect consistency for spreading.
Fold in the diced maraschino cherries. Use a spatula to delicately combine them, ensuring every bit of frosting is bursting with cherry goodness and visual charm.
Chill the frosting in the refrigerator for an hour to help firm it up. This step is optional but highly recommended for a better texture when frosting your baked goods.