Using a hand or stand mixer, mix together the sugar, butter, and shortening just until combined., With the mixer on medium speed, gradually add the extracts and the desired amount of water or milk. Less liquid will yield a stiffer frosting that will dry slightly and make cookies easier to stack; more will result in a softer, buttercream-like consistency, one that stays soft for several days., Beat on high speed until fluffy, 1 to 2 minutes. Remove from the mixer bowl, and use immediately; or store airtight at room temperature, until ready to frost cookies.