Every good Christmas cookie needs some good icing - we recommend pairing this with our Iced Shortbread Cookies, but it's good on sugar cookies as well.
Beat 1/4 cup softened unsalted butter, 1 1/2 cups (about 6 oz.) powdered sugar, 1/4 tsp. kosher salt, and 3 Tbsp. whole milk with an electric mixer on medium speed until blended. Gradually beat in 1 1 /2 cups (about 6 oz.) more powdered sugar and 1 more Tbsp. milk.